I2C for R-Car platforms

Required properties:
- compatible:
	"renesas,i2c-r8a7743" if the device is a part of a R8A7743 SoC.
	"renesas,i2c-r8a7745" if the device is a part of a R8A7745 SoC.
	"renesas,i2c-r8a7778" if the device is a part of a R8A7778 SoC.
	"renesas,i2c-r8a7779" if the device is a part of a R8A7779 SoC.
	"renesas,i2c-r8a7790" if the device is a part of a R8A7790 SoC.
	"renesas,i2c-r8a7791" if the device is a part of a R8A7791 SoC.
	"renesas,i2c-r8a7792" if the device is a part of a R8A7792 SoC.
	"renesas,i2c-r8a7793" if the device is a part of a R8A7793 SoC.
	"renesas,i2c-r8a7794" if the device is a part of a R8A7794 SoC.
	"renesas,i2c-r8a7795" if the device is a part of a R8A7795 SoC.
	"renesas,i2c-r8a7796" if the device is a part of a R8A7796 SoC.
	"renesas,rcar-gen1-i2c" for a generic R-Car Gen1 compatible device.
	"renesas,rcar-gen2-i2c" for a generic R-Car Gen2 or RZ/G1 compatible
				device.
	"renesas,rcar-gen3-i2c" for a generic R-Car Gen3 compatible device.
	"renesas,i2c-rcar" (deprecated)

	When compatible with the generic version, nodes must list the
	SoC-specific version corresponding to the platform first followed
	by the generic version.

- 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
  property indicates the default frequency 100 kHz.
- clocks: clock specifier.
- dmas: Must contain a list of two references to DMA specifiers, one for
  transmission, and one for reception.
- dma-names: Must contain a list of two DMA names, "tx" and "rx".

- i2c-scl-falling-time-ns: see i2c.txt
- i2c-scl-internal-delay-ns: see i2c.txt
- i2c-scl-rising-time-ns: see i2c.txt

Examples :

i2c0: i2c@e6508000 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "renesas,i2c-r8a7791", "renesas,rcar-gen2-i2c";
	reg = <0 0xe6508000 0 0x40>;
	interrupts = <0 287 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&mstp9_clks R8A7791_CLK_I2C0>;
	clock-frequency = <400000>;
};