iommu/mediatek: Remove mtk_iommu.h

Currently there is a suspend structure in the header file. It's no need
to keep a header file only for this. Move these into the c file and rm
this header file.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20220503071427.2285-28-yong.wu@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>