media: mediatek: vcodec: Extract H264 common code

Mt8192 can use some of common code with mt8183. Moves them to
a new file in order to reuse.

[hverkuil: replaced memcpy_toio by memcpy, was left over from a prev version]

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.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>