iommu/mediatek: Move inv_sel_reg into the plat_data

iommu/mediatek: Move inv_sel_reg into the plat_data

For mt6779, MMU_INV_SEL register's offset is changed from
0x38 to 0x2c, so we can put inv_sel_reg in the plat_data to
use it.
In addition, we renamed it to REG_MMU_INV_SEL_GEN1 and use it
before mt6779.

Signed-off-by: Chao Hao <chao.hao@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20200703044127.27438-6-chao.hao@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>