arm64: dts: mediatek: mt8173: 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/20220616110830.26037-4-angelogioacchino.delregno@collabora.comSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>

arch/arm64/boot/dts/mediatek/mt8173.dtsi

@@ -588,6 +588,7 @@ iommu: iommu@10205000 {
 			interrupts = <GIC_SPI 139 IRQ_TYPE_LEVEL_LOW>;
 			clocks = <&infracfg CLK_INFRA_M4U>;
 			clock-names = "bclk";
+			mediatek,infracfg = <&infracfg>;
 			mediatek,larbs = <&larb0>, <&larb1>, <&larb2>,
 					 <&larb3>, <&larb4>, <&larb5>;
 			#iommu-cells = <1>;