arm64: dts: mediatek: mt2712e: Add mediatek, infracfg phandle for IOMMU

The IOMMU driver now looks for the "mediatek,infracfg" phandle as a
new way to retrieve a syscon to that:
even though the old way is retained, it has been deprecated and the
driver will write a message in kmsg advertising to use the phandle
way instead.

For this reason, assign the right phandle to mediatek,infracfg in
the iommu node.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Miles Chen <miles.chen@mediatek.com>
Link: https://lore.kernel.org/r/20220616110830.26037-5-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>