ASoC: dt-bindings: rt9120: Add initial bindings

Add initial bindings for Richtek rt9120 audio amplifier.
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1634088519-995-2-git-send-email-u0084500@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/richtek,rt9120.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/richtek,rt9120.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT9120 Class-D audio amplifier
+
+maintainers:
+  - ChiYuan Huang <cy_huang@richtek.com>
+
+description: |
+  The RT9120 is a high efficiency, I2S-input, stereo audio power amplifier
+  delivering 2*20W into 8 Ohm BTL speaker loads. It supports the wide input
+  voltage  range from 4.5V to 26.4V to meet the need on most common
+  applications like as TV, monitors. home entertainment, electronic music
+  equipment.
+
+properties:
+  compatible:
+    enum:
+      - richtek,rt9120
+
+  reg:
+    description: I2C device address
+    maxItems: 1
+
+  pwdnn-gpios:
+    description: GPIO used for power down, low active
+    maxItems: 1
+
+  dvdd-supply:
+    description: |
+      Supply for the default on DVDD power, voltage domain must be 3P3V or 1P8V
+
+  '#sound-dai-cells':
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - dvdd-supply
+  - '#sound-dai-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      rt9120@1a {
+        compatible = "richtek,rt9120";
+        reg = <0x1a>;
+        pwdnn-gpios = <&gpio26 2 0>;
+        dvdd-supply = <&vdd_io_reg>;
+        #sound-dai-cells = <0>;
+      };
+    };