ARM: zynq: Add interrupt-controller property to gpio nodes

GPIO driver supports an input interrupt that's why gpio node itself can
be labeled as interrupt controller.
Reported-by: NJohn Linn <linnj@xilinx.com>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynq-7000.dtsi

@@ -96,8 +96,10 @@
 		gpio0: gpio@e000a000 {
 			compatible = "xlnx,zynq-gpio-1.0";
 			#gpio-cells = <2>;
+			#interrupt-cells = <2>;
 			clocks = <&clkc 42>;
 			gpio-controller;
+			interrupt-controller;
 			interrupt-parent = <&intc>;
 			interrupts = <0 20 4>;
 			reg = <0xe000a000 0x1000>;