media: coda: allow flagging last output buffer internally

Since V4L2_BUF_FLAG_LAST is a CAPTURE only flag, clear it from OUTPUT
buffers in QBUF and DQBUF. This allows to use the flag internally to
signal the last buffer to decode after a decoder stop command was
issued.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>