iommu/mediatek: Add mutex for data in the mtk_iommu_domain

iommu/mediatek: Add mutex for data in the mtk_iommu_domain

Same with the previous patch, add a mutex for the "data" in the
mtk_iommu_domain. Just improve the safety for multi devices
enter attach_device at the same time. We don't get the real issue
for this.

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/20220503071427.2285-9-yong.wu@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>