Device-Tree bindings for i2c gpio driver

Required properties:
	- compatible = "i2c-gpio";
	- gpios: sda and scl gpio


Optional properties:
	- i2c-gpio,sda-open-drain: sda as open drain
	- i2c-gpio,scl-open-drain: scl as open drain
	- i2c-gpio,scl-output-only: scl as output only
	- i2c-gpio,delay-us: delay between GPIO operations (may depend on each platform)
	- i2c-gpio,timeout-ms: timeout to get data

Example nodes:

i2c@0 {
	compatible = "i2c-gpio";
	gpios = <&pioA 23 0 /* sda */
		 &pioA 24 0 /* scl */
		>;
	i2c-gpio,sda-open-drain;
	i2c-gpio,scl-open-drain;
	i2c-gpio,delay-us = <2>;	/* ~100 kHz */
	#address-cells = <1>;
	#size-cells = <0>;

	rv3029c2@56 {
		compatible = "rv3029c2";
		reg = <0x56>;
	};
};