soc: mediatek: mmsys: Add reset controller support

Among other features the mmsys driver should implement a reset
controller to be able to reset different bits from their space.

Cc: Jitao Shi <jitao.shi@mediatek.com>
Suggested-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20210930103105.v4.6.I15e2419141a69b2e5c7e700c34d92a69df47e04d@changeid


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