minigbm: support NV12 in virtio_gpu

To use vivid on VM as an external camera, virtio_gpu has to support
NV12.

BUG=chromium:852302
TEST=Use camera app on betty by using vivid as an external camera
Change-Id: I84ddcbae473a06337918328afe1db8d32003ad84
Signed-off-by: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1160434
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
1 file changed