ASoC: dt-bindings: add dt bindings for adau1977 audio codec

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-gpio:  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

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>;

		reset_gpio = <&gpio 10 GPIO_ACTIVE_LOW>;

	};

	adau1977_i2c: adau1977@11 {

		compatible = "adi,adau1977";

		reg = <0x11>;

		AVDD-supply = <&regulator>;

		DVDD-supply = <&regulator_digital>;

		reset_gpio = <&gpio 10 GPIO_ACTIVE_LOW>;

	};