* ST SPEAr ADC device driver

Required properties:
- compatible: Should be "st,spear600-adc"
- reg: Address and length of the register set for the device
- interrupt-parent: Should be the phandle for the interrupt controller
  that services interrupts for this device
- interrupts: Should contain the ADC interrupt
- sampling-frequency: Default sampling frequency

Optional properties:
- vref-external: External voltage reference in milli-volts. If omitted
  the internal voltage reference will be used.
- average-samples: Number of samples to generate an average value. If
  omitted, single data conversion will be used.

Examples:

	adc: adc@d8200000 {
		compatible = "st,spear600-adc";
		reg = <0xd8200000 0x1000>;
		interrupt-parent = <&vic1>;
		interrupts = <6>;
		sampling-frequency = <5000000>;
		vref-external = <2500>;	/* 2.5V VRef */
	};