ARM: dts: imx6sx-sdb: add gpio key support

This patch adds support for imx6sx-sdb board's gpio keys:

SW4(FUNC1): KEY_VOLUMEUP
SW5(FUNC2): KEY_VOLUMEDOWN
Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/imx6sx-sdb.dts

@@ -8,6 +8,8 @@
 
 /dts-v1/;
 
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
 #include "imx6sx.dtsi"
 
 / {
@@ -22,6 +24,24 @@ memory {
 		reg = <0x80000000 0x40000000>;
 	};
 
+	gpio-keys {
+		compatible = "gpio-keys";
+		pinctrl-names = "default";
+		pinctrl-0 = <&pinctrl_gpio_keys>;
+
+		volume-up {
+			label = "Volume Up";
+			gpios = <&gpio1 18 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_VOLUMEUP>;
+		};
+
+		volume-down {
+			label = "Volume Down";
+			gpios = <&gpio1 19 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_VOLUMEDOWN>;
+		};
+	};
+
 	regulators {
 		compatible = "simple-bus";
 		#address-cells = <1>;
@@ -114,6 +134,13 @@ MX6SX_PAD_RGMII1_RX_CTL__ENET1_RX_EN	0x3081
 			>;
 		};
 
+		pinctrl_gpio_keys: gpio_keysgrp {
+			fsl,pins = <
+				MX6SX_PAD_CSI_DATA04__GPIO1_IO_18 0x17059
+				MX6SX_PAD_CSI_DATA05__GPIO1_IO_19 0x17059
+			>;
+		};
+
 		pinctrl_vcc_sd3: vccsd3grp {
 			fsl,pins = <
 				MX6SX_PAD_KEY_COL1__GPIO2_IO_11		0x17059