Add fallback path for drawing unsupported bitmap configs

Cherry-pick of https://skia-review.googlesource.com/c/skia/+/154180
to android/next-release. Second of two changes to support fallback
for uploading F16 bitmaps.

Just converts to RGBA_8888 before uploading.

No-Tree-Checks: true
No-Try: true
No-Presubmit: true
Bug: skia:8375
Change-Id: I7e323da51debb4950c17049ed3b4822a202cba73
Reviewed-On: https://skia-review.googlesource.com/154180
Reviewed-By: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-on: https://skia-review.googlesource.com/154622