media: v4l2-controls: Add control for background detection

media: v4l2-controls: Add control for background detection

Add a generic V4L2 boolean control V4L2_CID_MPEG_VIDEO_BACKGROUND_DETECTION
that allows encoders to detect background regions in a frame and use fewer
bits or skip mode to encode them, potentially reducing bitrate for streams
with stationary scenes.

Signed-off-by: Jackson Lee <jackson.lee@chipsnmedia.com>
Signed-off-by: Nas Chung <nas.chung@chipsnmedia.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>