Early instances of 'white person'
The earliest match for "white person" (in any sense of the term) that I've been able to find is from George Bate, The Lives, Actions, and Execution of the Prime Actors, and Principall Contrivers of That Horrid Murder of Our Late Pious and Sacred Soveraigne King Charles the First of Ever Blessed Memory (1661):
No Orthodox Minister could there [in Wales] be suffered, but whom he [Major General Harrison] pleased to allow; and with the assistance of his Chaplain Mr. Vavasor Powel, (a giddy-headed Parson, and second Brother to H. Peters) he endeavour's the modeling of that Countrey, so, as that none but their own proselytes should teach and instruct the people. In a word, he was the chief Holder forth to that dangerous people called Fifth Monarchiers, and the chief Incendiary to set foot, malignant and evil designs against the sacred Institution of Kings and Princes; and one that upon the trial of our most innocent Sovereign, used this expression, That they should blacken that white person as much as they could, in drawing up their charge against him.
Here the meaning of white is "pure, innocent, faultless, and exemplary"—an association presumably based on the fact that white surfaces show dirt, stains, and other blemishes more obviously than do other colored surfaces, so a truly white surface is noteworthy for its cleanness. There is no evident (or necessary) racial component to this usage.
A second instance of "white person" is reported in William Rawlin, The Laws of Barbados Collected in One Volume (1699). I don't have access to the full contents of this book, but the table of contents includes an entry for "An ACT for the speedy supply of Arms, Ammunition, Stores and white Servants," which suggests that the instance of "white person" is probably intended in an explicitly racial sense.
Early instances of 'white people'
The earliest match for "white people" that I've been able to find is from a 1555 translation by Rycharde Eden of Peter Martyr of Angleria, The decades of the newe worlde or west India conteynyng the nauigations and conquestes of the Spanyardes, with the particular description of the moste ryche and large landes and ilandes lately founde in the west ocean perteynyng to the inheritaunce of the kinges of Spayne:
Of these lands, Iacobus Gastaldus wryteth thus: The newe lande of Baccalaos [Cape Breton], is a coulde region, whose inhabytauntes are Idolatours and praye to the soonne and moon and dyuers Idoles. They are whyte people and very rustical. For they eate flesshe and fysshe and all other thynges rawe. Sumtymes also they eate mans flesshe priuilye so that theyr Laciqui haue no knowleage therof. The apparell of both the men and women, is made of beares skynnes, althowgh they haue sables and marternes, not greatly estemed bycause they are lyttle. Sum of them go naked in soommer, and weare apparell only in wynter. The Brytous and Frenche men are accustomed to take fysshe in the coaste of these landes where is founde great plentie of Tunnyes which thinhabitauntes caul Baccalaos wherof the lande was so named.
Anghiera died in 1526, so his use (in Latin) of "white people" is quite early. However, the usage here does not seem intended to indicate that the natives of Baccalaos are of European ancestry, but rather that they are light-skinned.
A second early instance of "white people" appears in a 1581 translation of Agustin de Zárate, The discouerie and conquest of the prouinces of Peru, and the nauigation in the South Sea, along that coast And also of the ritche mines of Potosi:
The Indians doth reporte than when Guascar saw that hée should die, hee said I haue béene a small while, Lord of this Land, and lesse shalbe the traytour my Brother, by whose commaundement I now must die, beeing his naturall Prince: the which his words were well remembred: for when they saw Atabaliba slaine, as in this nexte Chapter shalbe declared, they called to remembrance his wordes, and said verely, that Guascar was a Prophet, & childe of the Sunne, consideringe how his wordes came to passe, hee also sayd, that when his Father departed frō him, hee warned him, that whē a white people, bearded, should come into that Countrey, that hee should submit him selfe vnto them, because (said hee) they shalbe Lords ouer this Countrey, although this thy Fathers Prophesie seemed strange, yet through the industry of the Diuel it might be knowen, for so much it happen•d before Guaynacaua died.
The term "a white people" here is put into the mouth of the Inca sovereign Guascar, but it seems to indicate an racial or ethnic designation for an alien group of people.
A 1588 translation by R. Parke, of Juan González de Mendoza, The historie of the great and mightie kingdome of China, and the situation thereof togither with the great riches, huge citties, politike gouernement, and rare inuentions in the same offers this instance of the term in reference to the skin color of East Asian people in the vicinity of Canton, China:
There is séene great diuersities in the colours of such people as doo come thither to traficke, as the said Portingales do testifie.
Those which are borne in the citie of Canton and in al that cost are browne people, like vnto them in the citie of Fez or Barberie, for that all the whole countrie is in the said paralel that Barberie is in. And they of the most prouinces inwards are white people, some more whiter then others, as they draw into the cold countrie. Some are like vnto Spanyards, and others more yealow, like vnto the Almans, yelow and red colour.
And a companion 1588 translation by Parke of A Commentarie or short discourse of all such notable thinges as be betwixt Spaine till you come vnto the kingdome of China, and from China vnto Spaine, returning by the Orientall or east Indias, after that they had almost compassed the whole world. Wherein is contayned all the rites, ceremonies and customes of the people, the riches, fertilitie and strength of many kingdomes: and the description of them, perhaps by Martín Ignacio de Loyola (if I am reading the attributions correctly), offers multiple references to "white people" in reference to East Asian ethnic groups:
All these Ilands are inhabited with white people of comely faces, like vnto those of Europa, but not of their bodies, for that they are as bigge as gyants, and of so great force and strength : for one of them hath taken two Spaniardes, of a good stature, the one by one foot, and the other by the other, with his handes, and hath lifted them both from the grounde with so great ease, as though they had bin two children. They go naked from top to toe, as well women as men; yet some of them were woont to weare an apome made of a deares skinne before them of halfe a yeard long for honesties sake, but they are but a fewe in number, in respect of those that weare nothing before them.
This kingdome is vnder the tropike of Capricorne, and stretcheth foorth on the sea coast, south west and north east, more than fine hundreth leagues : it hath on the partes south west the kingdome of Cochinchina, and on the north east, it dooth confine on Tartarian a kingdome which dooth compasse the most part of the lande ; on the other part of the north-west there is an other mightie kingdome of white people, which is beyonde the kingdome of Persia, it is called Catay: there be in it Christians, and the king thereof is called Manuell.
They are verie white people of this kingdome, and are apparelled like vnto those of China: their women are verie honest and shamefast, and their apparell is very curious and gallant. The men weare their haire dispersed, and doo combe and trim it with too much care.
The China-focused instances of "white people" in these last two original sources are interesting because they use the term in what seems to be a purely descriptive way, with no hint that the authors view "white people" as a proprietary racial grouping that Europeans hold an exclusive right to.