ARM: dts: cubox: Map gpio-keys to gpio3 8

The Cubox has a recessed button between the HDMI and RJ-45 connectors
that wasn't mapped in the device tree, so I've mapped it to gpio-keys
BTN_0.
Signed-off-by: George Joseph <george.joseph@fairview5.com>
Tested-by: George Joseph <george.joseph@fairview5.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx6qdl-cubox-i.dtsi

@@ -41,6 +41,8 @@
  */
 #include "imx6qdl-microsom.dtsi"
 #include "imx6qdl-microsom-ar8035.dtsi"
+#include <dt-bindings/input/input.h>
+#include <dt-bindings/gpio/gpio.h>
 
 / {
 	ir_recv: ir-receiver {
@@ -104,6 +106,18 @@ sound-spdif {
 		spdif-controller = <&spdif>;
 		spdif-out;
 	};
+
+	gpio-keys {
+		compatible = "gpio-keys";
+		pinctrl-0 = <&pinctrl_gpio_key>;
+		pinctrl-names = "default";
+
+		button_0 {
+			label = "Button 0";
+			gpios = <&gpio3 8 GPIO_ACTIVE_LOW>;
+			linux,code = <BTN_0>;
+		};
+	};
 };
 
 &hdmi {
@@ -208,6 +222,12 @@ MX6QDL_PAD_SD2_DAT2__SD2_DATA2 0x17059
 				MX6QDL_PAD_SD2_DAT3__SD2_DATA3 0x13059
 			>;
 		};
+
+		pinctrl_gpio_key: gpio-key {
+			fsl,pins = <
+				MX6QDL_PAD_EIM_DA8__GPIO3_IO08	0x17059
+			>;
+		};
 	};
 };