dt-bindings: GPIO: Add TPIC2810 binding

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>;

	};