mt7622: linksys-e8450: enable using mt7531 switch irq

Turns out the MT7531 switch IRQ line is connected to GPIO#53 just like
on the BPi-R64, so this seems to be part of the reference design and
will probably apply to most MT7622+MT7531 boards.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/dts/mt7622-linksys-e8450.dtsi

@@ -144,6 +144,10 @@
 		switch@0 {
 			compatible = "mediatek,mt7531";
 			reg = <0>;
+			interrupt-controller;
+			#interrupt-cells = <1>;
+			interrupt-parent = <&pio>;
+			interrupts = <53 IRQ_TYPE_LEVEL_HIGH>;
 			reset-gpios = <&pio 54 0>;
 
 			ports {