media: iris: add support for drain sequence

handle the V4L2_DEC_CMD_STOP by initiating a drain sequence on the
firmware. Process and decode all OUTPUT buffers, that are  queued by the
client, before the VIDIOC_DECODER_CMD() was issued and mark the last
buffer with the V4L2_BUF_FLAG_LAST flag. The decoder is stopped, after
processing the last buffer.

Resume the decoder when one of these operations are issued by the client:
- V4L2_DEC_CMD_START
- pair of VIDIOC_STREAMOFF() and VIDIOC_STREAMON() on the CAPTURE queue
- pair of VIDIOC_STREAMOFF() and VIDIOC_STREAMON() on the OUTPUT queue

Add the handling to resume decoding when client issues
V4L2_DEC_CMD_START to resume decoding after a source change is detected.

Tested-by: Stefan Schmidt <stefan.schmidt@linaro.org> # x1e80100 (Dell XPS 13 9345)
Reviewed-by: Stefan Schmidt <stefan.schmidt@linaro.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-HDK
Signed-off-by: Dikshita Agarwal <quic_dikshita@quicinc.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>