Device tree configuration for Renesas IIC (sh_mobile) driver

Required properties:
- compatible      : "renesas,iic-<soctype>". "renesas,rmobile-iic" as fallback
- reg             : address start and address range size of device
- interrupts      : interrupt of device
- clocks          : clock for device
- #address-cells  : should be <1>
- #size-cells     : should be <0>

Optional properties:
- clock-frequency : frequency of bus clock in Hz. Default 100kHz if unset.

Pinctrl properties might be needed, too. See there.

Example:

	iic0: i2c@e6500000 {
		compatible = "renesas,iic-r8a7790", "renesas,rmobile-iic";
		reg = <0 0xe6500000 0 0x425>;
		interrupts = <0 174 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&mstp3_clks R8A7790_CLK_IIC0>;
		clock-frequency = <400000>;
		#address-cells = <1>;
		#size-cells = <0>;
	};
