media: amphion: encoder copy timestamp from output to capture

copy the timestamp using the helper function
V4L2_BUF_FLAG_TIMESTAMP_COPY

To implement this, driver will keep the output buffer until it's
encoded, in previous, driver will return the output buffer immediately
after firmware return it

Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>