ASoC: cs4234: Add dtschema binding document

Document the bindings for the CS4234 ASoC codec driver.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20200928111821.26967-1-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/cirrus,cs4234.yaml

+# SPDX-License-Identifier: (GPL-2.0+ OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/cirrus,cs4234.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Cirrus Logic cs4234 audio CODEC
+
+maintainers:
+  - patches@opensource.cirrus.com
+
+description:
+  The CS4234 is a highly versatile CODEC that combines 4 channels of
+  high performance analog to digital conversion, 4 channels of high
+  performance digital to analog conversion for audio, and 1 channel of
+  digital to analog conversion to provide a nondelayed audio reference
+  signal to an external Class H tracking power supply. If not used to
+  drive a tracking power supply, the 5th DAC can instead be used as a
+  standard audio grade DAC, with performance specifications identical
+  to that of the 4 DACs in the audio path. Additionally, the CS4234
+  includes tunable group delay for each of the 4 audio DAC paths to
+  provide lead time for the external switch-mode power supply, and a
+  nondelayed path into the DAC outputs for input signals requiring a
+  low-latency path to the outputs.
+
+properties:
+  compatible:
+    enum:
+      - cirrus,cs4234
+
+  reg:
+    description:
+      The 7-bit I2C address depends on the state of the ADx pins, in
+      binary given by [0 0 1 0 AD2 AD1 AD0 0].
+    items:
+      minimum: 0x10
+      maximum: 0x17
+
+  VA-supply:
+    description:
+      Analogue power supply.
+
+  VL-supply:
+    description:
+      Interface power supply.
+
+  reset-gpios:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - VA-supply
+  - VL-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c@e0004000 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        reg = <0xe0004000 0x1000>;
+
+        cs4234: codec@11 {
+            compatible = "cirrus,cs4234";
+            reg = <0x11>;
+
+            VA-supply = <&vdd3v3>;
+            VL-supply = <&vdd3v3>;
+
+            reset-gpios = <&gpio 0>;
+        };
+    };