[media] coda: implement encoder stop command

There is no need to call v4l2_m2m_try_schedule to kick off draining the
bitstream buffer for the encoder, but we have to wake up the destination
queue in case there are no new OUTPUT buffers to be encoded and userspace
is already polling for new CAPTURE buffers.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>