Analog Devices ADAU1977/ADAU1978/ADAU1979

Datasheets:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1977.pdf
http://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1978.pdf
http://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1979.pdf

This driver supports both the I2C and SPI bus.

Required properties:
 - compatible: Should contain one of the following:
               "adi,adau1977"
               "adi,adau1978"
               "adi,adau1979"

 - AVDD-supply: analog power supply for the device, please consult
                Documentation/devicetree/bindings/regulator/regulator.txt

Optional properties:
 - reset-gpios: the reset pin for the chip, for more details consult
                Documentation/devicetree/bindings/gpio/gpio.txt

 - DVDD-supply: supply voltage for the digital core, please consult
                Documentation/devicetree/bindings/regulator/regulator.txt

- adi,micbias: configures the voltage setting for the MICBIAS pin.
		Select 0/1/2/3/4/5/6/7/8 to specify MICBIAS voltage
		5V/5.5V/6V/6.5V/7V/7.5V/8V/8.5V/9V
		If not specified the default value will be "7" meaning 8.5 Volts.
		This property is only valid for the ADAU1977

For required properties on SPI, please consult
Documentation/devicetree/bindings/spi/spi-bus.txt

Required properties on I2C:

 - reg:         The i2c address. Value depends on the state of ADDR0
                and ADDR1, as wired in hardware.

Examples:

	adau1977_spi: adau1977@0 {
		compatible = "adi,adau1977";
		spi-max-frequency = <600000>;

		AVDD-supply = <&regulator>;
		DVDD-supply = <&regulator_digital>;

		adi,micbias = <3>;
		reset-gpios = <&gpio 10 GPIO_ACTIVE_LOW>;
	};

	adau1977_i2c: adau1977@11 {
		compatible = "adi,adau1977";
		reg = <0x11>;

		AVDD-supply = <&regulator>;
		DVDD-supply = <&regulator_digital>;

		reset-gpios = <&gpio 10 GPIO_ACTIVE_LOW>;
	};
