arm64: zynqmp: Add missing gpio property to dtsi

All gpio controllers should contain this property.
This property is not checked by the code that's why this issue wasn't
found earlier.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynqmp.dtsi

@@ -672,6 +672,7 @@
 			interrupt-controller;
 			#interrupt-cells = <2>;
 			reg = <0x0 0xff0a0000 0x0 0x1000>;
+			gpio-controller;
 			power-domains = <&pd_gpio>;
 		};