ARM: dts: am335x: Enable gpio controller for GPMC

GPMC driver provides GPI support for the GPMC_WAIT pins.
Mark it gpio controller capable.
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am33xx.dtsi

@@ -868,6 +868,8 @@ gpmc: gpmc@50000000 {
 			#size-cells = <1>;
 			interrupt-controller;
 			#interrupt-cells = <2>;
+			gpio-controller;
+			#gpio-cells = <2>;
 			status = "disabled";
 		};