v4l2_stateful_encoder: implement drain

Make sure all the buffers are flushed
and the queues are stopped.

BUG=b:182200028
BUG=b:180448764
TEST=kukui and trogdor encode with no hard crash

Change-Id: Ia0580cdf281c2b6714c1fd2869a0277753c1d8fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/drm-tests/+/2757847
Tested-by: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Steve Cho <stevecho@chromium.org>
1 file changed