Alternatives to RGB24 and AYUV for working with GPU.

BUG=libyuv:832
TESTED=out/Release/libyuv_unittest --gtest_filter=*NV21To???24* --libyuv_width=1280 --libyuv_height=720 --libyuv_repeat=1000 --libyuv_flags=-1 --libyuv_cpu_info=-1
R=rrwinterton@gmail.com

Change-Id: I5559c63f4bd4c847492fcb1571f7b03c58146689
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/1501735Reviewed-by: richard winterton <rrwinterton@gmail.com>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>