iommu/mediatek: Add flag for legacy ivrp paddr

Add a new flag in order to select which IVRP_PADDR format is used
by an SoC.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20200907101649.1573134-2-fparent@baylibre.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>