gpio: tps65086: Add DT bindings for the TPS65086 GPO controller

The TPS65086 PMIC contains several regulators and a GPO controller.
Add bindings for the TPS65086 GPO controller.
Signed-off-by: NAndrew F. Davis <afd@ti.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-tps65086.txt

+* TPS65086 GPO Controller bindings
+
+Required properties:
+ - compatible		: Should be "ti,tps65086-gpio".
+ - gpio-controller	: Marks the device node as a GPIO Controller.
+ - #gpio-cells		: Should be two. The first cell is the pin number
+			    and the second cell is used to specify flags.
+			    See ../gpio/gpio.txt for possible values.
+
+Example:
+
+	gpio4: gpio {
+		compatible = "ti,tps65086-gpio";
+		gpio-controller;
+		#gpio-cells = <2>;
+	};