Refactor GrUploadPixmap logic into MakeCrossContextFromPixmap

MakeCrossContextPixmap was the only place we were using the helper in
SkGr, so this just shifts the logic into MakeCrosscontextFromPixmap.

Bug: skia:
Change-Id: I90126227ebacf889f9899ef7af9608a5664c582d
Reviewed-on: https://skia-review.googlesource.com/106280
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
3 files changed