ASoC: Add ADAU7002 Stereo PDM-to-I2S/TDM Converter DT bindings

The ADAU7002 takes a stereo PDM signal (e.g. from two digital microphones)
and converts it into a I2S/TDM PCM stream. The chip does not have a
control interface and has a single power supply that is modeled in the
devicetree.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/adi,adau7002.txt

+Analog Devices ADAU7002 Stereo PDM-to-I2S/TDM Converter
+
+Required properties:
+
+ - compatible: Must be "adi,adau7002"
+
+Optional properties:
+
+ - IOVDD-supply: Phandle and specifier for the power supply providing the IOVDD
+	supply as covered in Documentation/devicetree/bindings/regulator/regulator.txt
+
+	If this property is not present it is assumed that the supply pin is
+	hardwired to always on.
+
+Example:
+	adau7002: pdm-to-i2s {
+		compatible = "adi,adau7002";
+		IOVDD-supply = <&supply>;
+	};