dt-bindings: GPIO: Add TPIC2810 binding

Add binding for TPIC2810 GPO device.
Signed-off-by: NAndrew F. Davis <afd@ti.com>
Signed-off-by: NRoger Quadros <rogerq@ti.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-tpic2810.txt

+TPIC2810 GPIO controller bindings
+
+Required properties:
+ - compatible		: Should be "ti,tpic2810".
+ - reg			: The I2C address of the device
+ - gpio-controller	: Marks the device node as a GPIO controller.
+ - #gpio-cells		: Should be two. For consumer use see gpio.txt.
+
+Example:
+
+	gpio@60 {
+		compatible = "ti,tpic2810";
+		reg = <0x60>;
+		gpio-controller;
+		#gpio-cells = <2>;
+	};