VESA: move pixel formatting into __vesacon_copy_to_screen()

VESA: move pixel formatting into __vesacon_copy_to_screen()

Make pixel formatting an integral part of __vesacon_copy_to_screen().
In order to cut down on the dispatch overhead, make the formatting
functions contain the pixel loop, so we only do indirect dispatch
twice per pixel row - once for the formatting and once for copying to
the screen.