Nuvoton NPCM7XX I2C bus

The NPCM750x includes sixteen I2C bus controllers. All Controllers support
both master and slave mode. Each controller has two 16 byte HW FIFO for TX and
RX.

Required properties:
- compatible      : must be "nuvoton,npcm750-i2c"
- reg             : Offset and length of the register set for the device.
- interrupts      : Contain the I2C interrupt with flags for falling edge.
- clocks          : phandle of I2C reference clock.

Optional:
- bus-frequency   : Contain the I2C bus frequency,
			the default I2C bus frequency is 100000.
- pinctrl-0       : must be <&smbX_pins>, X is module number
			(on NPCM7XX it's 0 to 15)
- pinctrl-names   : should be set to "default"
Example:

	i2c0: i2c@80000 {
		compatible = "nuvoton,npcm750-i2c";
		reg = <0x80000 0x1000>;
		clocks = <&clk NPCM7XX_CLK_APB2>;
		bus-frequency = <100000>;
		interrupts = <GIC_SPI 64 IRQ_TYPE_LEVEL_HIGH>;
		pinctrl-names = "default";
		pinctrl-0 = <&smb0_pins>;
	};