I2C for R-Car platforms

Required properties:
- compatible: Must be one of
	"renesas,i2c-rcar"
	"renesas,i2c-r8a7778"
	"renesas,i2c-r8a7779"
	"renesas,i2c-r8a7790"
- reg: physical base address of the controller and length of memory mapped
  region.
- interrupts: interrupt specifier.

Optional properties:
- clock-frequency: desired I2C bus clock frequency in Hz. The absence of this
  propoerty indicates the default frequency 100 kHz.

Examples :

i2c0: i2c@e6500000 {
	compatible = "renesas,i2c-rcar-h2";
	reg = <0 0xe6500000 0 0x428>;
	interrupts = <0 174 0x4>;
};