staging: mt7621-dts: add missing properties to gpio node

In order to let other devices reference the GPIO interrupts
if necessary properties 'interrupt-controller' and
'#interrupt-cells' becomes necessary. Add both of them to
complete gpio device tree node.
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-dts/mt7621.dtsi

@@ -69,6 +69,8 @@ gpio@600 {
 
 			interrupt-parent = <&gic>;
 			interrupts = <GIC_SHARED 12 IRQ_TYPE_LEVEL_HIGH>;
+			interrupt-controller;
+			#interrupt-cells = <1>;
 
 			gpio0: bank@0 {
 				reg = <0>;