media: mtk-vcodec: enable MT8183 decoder

Now that all the supporting blocks are present, enable decoder for
MT8183.

[acourbot: refactor, cleanup and split]

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>