gpio: add bindings for Technologic I2C-FPGA gpio controller

* Technologic Systems I2C-FPGA's GPIO controller bindings

This bindings describes the GPIO controller for Technologic's FPGA core.

TS-4900's FPGA encodes the GPIO state on 3 bits, whereas the TS-7970's FPGA

uses 2 bits: it doesn't use a dedicated input bit.

Required properties:

- compatible: Should be one of the following

		"technologic,ts4900-gpio"

		"technologic,ts7970-gpio"

- reg: Physical base address of the controller and length

       of memory mapped region.

- #gpio-cells: Should be two. The first cell is the pin number.

- gpio-controller: Marks the device node as a gpio controller.

Optional property:

- ngpios: Number of GPIOs this controller is instantiated with,

  the default is 32. See gpio.txt for more details.

Example:

&i2c2 {

	gpio8: gpio@28 {

		compatible = "technologic,ts4900-gpio";

		reg = <0x28>;

		#gpio-cells = <2>;

		gpio-controller;

		ngpios = <32>;

	};

};