iommu/mediatek: Add a flag for iova 34bits case

Add a HW flag for if the HW support 34bit IOVA. the previous SoC
still use 32bit. normally the lvl1 pgtable size is 16KB when ias == 32.
if ias == 34, lvl1 pgtable size is 16KB * 4. The purpose of this patch
is to save 16KB*3 continuous memory for the previous SoC.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Link: https://lore.kernel.org/r/20210111111914.22211-15-yong.wu@mediatek.com
Signed-off-by: Will Deacon <will@kernel.org>