Device-Tree bindings for i2c gpio driver

Required properties:
	- compatible = "i2c-gpio";
	- sda-gpios: gpio used for the sda signal, this should be flagged as
	  active high using open drain with (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)
	  from <dt-bindings/gpio/gpio.h> since the signal is by definition
	  open drain.
	- scl-gpios: gpio used for the scl signal, this should be flagged as
	  active high using open drain with (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)
	  from <dt-bindings/gpio/gpio.h> since the signal is by definition
	  open drain.

Optional properties:
	- 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

Deprecated properties, do not use in new device tree sources:
	- gpios: sda and scl gpio, alternative for {sda,scl}-gpios
	- i2c-gpio,sda-open-drain: this means that something outside of our
	  control has put the GPIO line used for SDA into open drain mode, and
	  that something is not the GPIO chip. It is essentially an
	  inconsistency flag.
	- i2c-gpio,scl-open-drain: this means that something outside of our
	  control has put the GPIO line used for SCL into open drain mode, and
	  that something is not the GPIO chip. It is essentially an
	  inconsistency flag.

Example nodes:

#include <dt-bindings/gpio/gpio.h>

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

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