soc: mediatek: mmsys: Create struct mtk_mmsys to store context data

Apart from the driver data, in order to extend the driver to support more
and more SoCs, we will need to store other configuration data. So, create
a mtk_mmsys struct to encapsulate all that information.

Signed-off-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20210317181711.795245-2-enric.balletbo@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>