ASoC: pcm3168a: Add binding document for pcm3168a codec

Add binding document for Texas Instruments pcm3168a codec
Signed-off-by: Damien.Horsley <Damien.Horsley@imgtec.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/ti,pcm3168a.txt

+Texas Instruments pcm3168a DT bindings
+
+This driver supports both SPI and I2C bus access for this codec
+
+Required properties:
+
+  - compatible: "ti,pcm3168a"
+
+  - clocks : Contains an entry for each entry in clock-names
+
+  - clock-names : Includes the following entries:
+	"scki"	The system clock
+
+  - VDD1-supply : Digital power supply regulator 1 (+3.3V)
+
+  - VDD2-supply : Digital power supply regulator 2 (+3.3V)
+
+  - VCCAD1-supply : ADC power supply regulator 1 (+5V)
+
+  - VCCAD2-supply : ADC power supply regulator 2 (+5V)
+
+  - VCCDA1-supply : DAC power supply regulator 1 (+5V)
+
+  - VCCDA2-supply : DAC power supply regulator 2 (+5V)
+
+For required properties on SPI/I2C, consult SPI/I2C device tree documentation
+
+Examples:
+
+i2c0: i2c0@0 {
+
+	...
+
+	pcm3168a: audio-codec@44 {
+		compatible = "ti,pcm3168a";
+		reg = <0x44>;
+		clocks = <&clk_core CLK_AUDIO>;
+		clock-names = "scki";
+		VDD1-supply = <&supply3v3>;
+		VDD2-supply = <&supply3v3>;
+		VCCAD1-supply = <&supply5v0>;
+		VCCAD2-supply = <&supply5v0>;
+		VCCDA1-supply = <&supply5v0>;
+		VCCDA2-supply = <&supply5v0>;
+		pinctrl-names = "default";
+		pinctrl-0 = <&dac_clk_pin>;
+	};
+};