media: mediatek: vcodec: Removing struct 'mtk_vcodec_ctx/dev' for shared interface

The shared struct 'mtk_vcodec_ctx/dev' will be changed to
'mtk_vcodec_enc_ctx/dev' and 'mtk_vcodec_dec_ctx/dev' in order to separate
encoder and decoder. Removing common struct 'mtk_vcodec_ctx/dev' for shared
interface which encoder and decoder used at the same time. Then encoder and
decoder can call the same interface independently.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>