dt-bindings: iommu: mediatek: Add mediatek,infracfg phandle

Add property "mediatek,infracfg" to let the mtk_iommu driver retrieve
a phandle to the infracfg syscon instead of performing a per-soc
compatible lookup in the entire devicetree and set it as a required
property for MT2712 and MT8173.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20220616110830.26037-2-angelogioacchino.delregno@collabora.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>