Documentation: dt-bindings: Document bindings for Aspeed ADC

Aspeed ADC

This device is a 10-bit converter for 16 voltage channels.  All inputs are

single ended.

Required properties:

- compatible: Should be "aspeed,ast2400-adc" or "aspeed,ast2500-adc"

- reg: memory window mapping address and length

- clocks: Input clock used to derive the sample clock. Expected to be the

          SoC's APB clock.

- #io-channel-cells: Must be set to <1> to indicate channels are selected

                     by index.

Example:

	adc@1e6e9000 {

		compatible = "aspeed,ast2400-adc";

		reg = <0x1e6e9000 0xb0>;

		clocks = <&clk_apb>;

		#io-channel-cells = <1>;

	};