ASoC: Add bindings for PCM1789

Add a device-tree binding for Texas Instrument's PCM1789 codec.
For the moment, only I2C bus is supported but SPI could be added
in future.
Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/pcm1789.txt

+Texas Instruments pcm1789 DT bindings
+
+PCM1789 is a simple audio codec that can be connected via
+I2C or SPI. Currently, only I2C bus is supported.
+
+Required properties:
+
+ - compatible: "ti,pcm1789"
+
+Required properties on I2C:
+
+ - reg: the I2C address
+ - reset-gpios: GPIO to control the RESET pin
+
+Examples:
+
+	audio-codec@4c {
+		compatible = "ti,pcm1789";
+		reg = <0x4c>;
+		reset-gpios = <&gpio2 14 GPIO_ACTIVE_LOW>;
+		#sound-dai-cells = <0>;
+	};