media: venus: reimplement decoder stop command

This addresses the wrong behavior of decoder stop command by
rewriting it. These new implementation enqueue an empty buffer
on the decoder input buffer queue to signal end-of-stream. The
client should stop queuing buffers on the V4L2 Output queue
and continue queuing/dequeuing buffers on Capture queue. This
process will continue until the client receives a buffer with
V4L2_BUF_FLAG_LAST flag raised, which means that this is last
decoded buffer with data.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Tested-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v4.13 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>