iommu/mediatek: Update oas for v7s

This patch only updates oas in different SoCs.

If the SoC supports 4GB-mode and current dram size is 4GB, the oas is 33.
otherwise, it's still 32. In the lastest SoC, the oas is 35bits.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Link: https://lore.kernel.org/r/20210111111914.22211-16-yong.wu@mediatek.com
Signed-off-by: Will Deacon <will@kernel.org>