Phytium ADC

This device is a 10-bit converter for 8 voltage channels. All inputs are
single ended.

Required properties:
- compatible: Should be "phytium,adc"
- reg: memory window mapping address and length
- interrupts: Interrupt for the ADC control interface.
- clocks: Input clock used to derive the sample clock.
- #address-cells: Should be <1> (settings for the subnodes).
- #size-cells: Should be <0> (settings for the subnodes).

Required subnodes:

The ADC channels are configured as subnodes of the ADC.

Required channel node properties:

- reg: should contain the hardware channel number.

Examples:

	adc0: adc@2807b000 {
		compatible = "phytium,adc";
		reg = <0x0 0x2807b000 0x0 0x1000>;
		interrupts = <GIC_SPI 232 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&sysclk_48mhz>;

		#address-cells = <1>;
		#size-cells = <0>;

		channel@0 {
			reg = <0>;
		};
		channel@1 {
			reg = <1>;
		};
		channel@2 {
			reg = <2>;
		};
		channel@3 {
			reg = <3>;
		};
		channel@4 {
			reg = <4>;
		};
		channel@5 {
			reg = <5>;
		};
		channel@6 {
			reg = <5>;
		};
		channel@7 {
			reg = <7>;
		};
	};
