media: mediatek: vcodec: support stateless hevc decoder

Add mediatek hevc decoder linux driver which use the stateless API in
MT8195.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Nathan Hebert <nhebert@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: add () around 'flag' in macro]