iommu/mediatek: Backup/restore regsiters for multi banks

Each bank has some independent registers. thus backup/restore them for
each a bank when suspend and resume.

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/20220503071427.2285-35-yong.wu@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>