media: mediatek: vcodec: Refactor get and put capture buffer flow

For lat and core decode in parallel, need to get capture buffer
when core start to decode and put capture buffer to display
list when core decode done.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>