ARM: mvebu: Add button on Armada 370 Reference Design board

The Marvell Armada 370 Reference Design board has a software-controlled
button on the front side, marked as "SW".
This patch adds minimal support for this button.
Signed-off-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: NFlorian Fainelli <florian@openwrt.org>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>

arch/arm/boot/dts/armada-370-rd.dts

@@ -65,4 +65,15 @@
 			/* No CD or WP GPIOs */
 		};
 	};
+
+	gpio-keys {
+		compatible = "gpio-keys";
+		#address-cells = <1>;
+		#size-cells = <0>;
+		button@1 {
+			label = "Software Button";
+			linux,code = <116>;
+			gpios = <&gpio0 6 1>;
+		};
+	};
 };