Maxim max5821 DAC device driver

Required properties:
	- compatible: Must be "maxim,max5821"
	- reg: Should contain the DAC I2C address
	- vref-supply: Phandle to the vref power supply

Example:

	max5821@38 {
		compatible = "maxim,max5821";
		reg = <0x38>;
		vref-supply = <&reg_max5821>;
	};