I2C for R-Car platforms

Required properties:
- compatible: Must be one of
	"renesas,i2c-rcar"
	"renesas,i2c-r8a7778"
	"renesas,i2c-r8a7779"
	"renesas,i2c-r8a7790"
	"renesas,i2c-r8a7791"
	"renesas,i2c-r8a7792"
	"renesas,i2c-r8a7793"
	"renesas,i2c-r8a7794"
	"renesas,i2c-r8a7795"
	"renesas,i2c-r8a7796"
- 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";
	reg = <0 0xe6508000 0 0x40>;
	interrupts = <0 287 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&mstp9_clks R8A7791_CLK_I2C0>;
	clock-frequency = <400000>;
};