Nuvoton NPCM Analog to Digital Converter (ADC)

The NPCM ADC is a 10-bit converter for eight channel inputs.

Required properties:
- compatible: "nuvoton,npcm750-adc" for the NPCM7XX BMC.
- reg: specifies physical base address and size of the registers.
- interrupts: Contain the ADC interrupt with flags for falling edge.

Optional properties:
- clocks: phandle of ADC reference clock, in case the clock is not
		  added the ADC will use the default ADC sample rate.
- vref-supply: The regulator supply ADC reference voltage, in case the
			   vref-supply is not added the ADC will use internal voltage
			   reference.

Example:

adc: adc@f000c000 {
	compatible = "nuvoton,npcm750-adc";
	reg = <0xf000c000 0x8>;
	interrupts = <GIC_SPI 0 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clk NPCM7XX_CLK_ADC>;
};