ASoC: cs43130: Add devicetree bindings for CS43130

Add devicetree bindings documentation file for Cirrus
Logic CS43130 codec.
Signed-off-by: Li Xu <li.xu@cirrus.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/cs43130.txt

+CS43130 DAC
+
+Required properties:
+
+  - compatible : "cirrus,cs43130", "cirrus,cs4399", "cirrus,cs43131",
+                 "cirrus,cs43198"
+
+  - reg : the I2C address of the device for I2C
+
+  - VA-supply, VP-supply, VL-supply, VCP-supply, VD-supply:
+	power supplies for the device, as covered in
+	Documentation/devicetree/bindings/regulator/regulator.txt.
+
+
+Optional properties:
+
+  - reset-gpios : Active low GPIO used to reset the device
+
+  - cirrus,xtal-ibias:
+   When external MCLK is generated by external crystal
+   oscillator, CS43130 can be used to provide bias current
+   for external crystal.  Amount of bias current sent is
+   set as:
+   1 = 7.5uA
+   2 = 12.5uA
+   3 = 15uA
+
+  - cirrus,dc-measure:
+   Boolean, define to enable headphone DC impedance measurement.
+
+  - cirrus,ac-measure:
+   Boolean, define to enable headphone AC impedance measurement.
+   DC impedance must also be enabled for AC impedance measurement.
+
+  - cirrus,dc-threshold:
+   Define 2 DC impedance thresholds in ohms for HP output control.
+   Default values are 50 and 120 Ohms.
+
+  - cirrus,ac-freq:
+   Define the frequencies at which to measure HP AC impedance.
+   Only used if "cirrus,dc-measure" is defined.
+   Exactly 10 frequencies must be defined.
+   If this properties is undefined, by default,
+   following frequencies are used:
+   <24 43 93 200 431 928 2000 4309 9283 20000>
+   The above frequencies are logarithmically equally spaced.
+   Log base is 10.
+
+Example:
+
+cs43130: audio-codec@30 {
+   compatible = "cirrus,cs43130";
+   reg = <0x30>;
+   reset-gpios = <&axi_gpio 54 0>;
+   VA-supply = <&dummy_vreg>;
+   VP-supply = <&dummy_vreg>;
+   VL-supply = <&dummy_vreg>;
+   VCP-supply = <&dummy_vreg>;
+   VD-supply = <&dummy_vreg>;
+   cirrus,xtal-ibias = <2>;
+   interrupt-parent = <&gpio0>;
+   interrupts = <55 8>;
+   cirrus,dc-measure;
+   cirrus,ac-measure;
+   cirrus,dc-threshold = /bits/ 16 <20 100>;
+   cirrus,ac-freq = /bits/ 16 <24 43 93 200 431 928 2000 4309 9283 20000>;
+};