Device tree configuration for i2c-ocores

Required properties:
- compatible      : "opencores,i2c-ocores"
- reg             : bus address start and address range size of device
- interrupts      : interrupt number
- clock-frequency : frequency of bus clock in Hz
- #address-cells  : should be <1>
- #size-cells     : should be <0>

Optional properties:
- reg-shift       : device register offsets are shifted by this value
- reg-io-width    : io register width in bytes (1, 2 or 4)
- regstep         : deprecated, use reg-shift above

Example:

	i2c0: ocores@a0000000 {
		#address-cells = <1>;
		#size-cells = <0>;
		compatible = "opencores,i2c-ocores";
		reg = <0xa0000000 0x8>;
		interrupts = <10>;
		clock-frequency = <20000000>;

		reg-shift = <0>;	/* 8 bit registers */
		reg-io-width = <1>;	/* 8 bit read/write */

		dummy@60 {
			compatible = "dummy";
			reg = <0x60>;
		};
	};
