kernel: backport MT7530 IRQ support

Support MT7530 PHY link change interrupts, and enable for MT7621.

For external MT7530, a GPIO IRQ line is required, which is
board-specific, so it should be added to each DTS. In case the
interrupt-controller property is missing, it will fall back to
polling mode.

Signed-off-by: DENG Qingfang <dqfext@gmail.com>

target/linux/ramips/dts/mt7621.dtsi

@@ -487,6 +487,9 @@
 				mediatek,mcm;
 				resets = <&rstctrl 2>;
 				reset-names = "mcm";
+				interrupt-controller;
+				#interrupt-cells = <1>;
+				interrupts = <GIC_SHARED 23 IRQ_TYPE_LEVEL_HIGH>;
 
 				ports {
 					#address-cells = <1>;