media: mtk-vcodec: vdec: support stateless H.264 decoding

Add support for H.264 decoding using the stateless API, as supported by
MT8183. This support takes advantage of the V4L2 H.264 reference list
builders.

[acourbot: refactor, cleanup and split]
[tzungbi: fix missing kerneldoc issue]
[hverkuil: fix trivial kerneldoc typo]

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Co-developed-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>