amdgpu: Enable to allocate YVU420 buffer with BO_USE_TEXTURE_MASK flag

amdgpu: Enable to allocate YVU420 buffer with BO_USE_TEXTURE_MASK flag

Chrome needs to allocate YUV420 buffer that cpu can read and write with a linear
view. YUV420 is not supported by gbm widely. YVU420 is used on behalf of YUV420.
This CL adds YVU420 to texture_source_formats so that YVU420 buffer can be
allocated on AMD platform.

BUG=chromium:987860
TEST=None

Change-Id: I11af92e74ad1d3c7c5631e67c5a2fef90077d887
Reviewed-on: https://chromium-review.googlesource.com/1728730
Tested-by: Hirokazu Honda <hiroh@chromium.org>
Commit-Ready: Hirokazu Honda <hiroh@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>