Implement more SkImage_GpuYUVA functionality

Bug: skia:7901
Change-Id: I78a947edb924e0a1240537a83aa0bc111239e567
Reviewed-on: https://skia-review.googlesource.com/c/159320
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
9 files changed