[graphite] Add more Metal backend textures

I noticed we weren't supporting 4444 while triaging the dithering changes. The other 6 are used for YUV textures.

Change-Id: I950e17fcc22a54046dacad17a307ae2dcf7bc951
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/660382
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
3 files changed