soc: mediatek: mtk-mmsys: Use module_platform_driver() macro

Instead of open-coding init/exit calls, switch to using the
module_platform_driver() macro instead, doing the exact same.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230222094253.23678-3-angelogioacchino.delregno@collabora.com


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