ASoC: dt-bindings: Add support for Loongson audio card

The audio card uses loongson I2S controller present in
7axxx/2kxxx chips to transfer audio data.

On loongson platform, the chip has only one I2S controller.
Signed-off-by: Yingkun Meng <mengyingkun@loongson.cn>
Link: https://lore.kernel.org/r/20230614122659.3402788-1-mengyingkun@loongson.cnSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/loongson,ls-audio-card.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/loongson,ls-audio-card.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Loongson 7axxx/2kxxx ASoC audio sound card driver
+
+maintainers:
+  - Yingkun Meng <mengyingkun@loongson.cn>
+
+description:
+  The binding describes the sound card present in loongson
+  7axxx/2kxxx platform. The sound card is an ASoC component
+  which uses Loongson I2S controller to transfer the audio data.
+
+properties:
+  compatible:
+    const: loongson,ls-audio-card
+
+  model:
+    $ref: /schemas/types.yaml#/definitions/string
+    description: User specified audio sound card name
+
+  mclk-fs:
+    $ref: simple-card.yaml#/definitions/mclk-fs
+
+  cpu:
+    description: Holds subnode which indicates cpu dai.
+    type: object
+    additionalProperties: false
+    properties:
+      sound-dai:
+        maxItems: 1
+    required:
+      - sound-dai
+
+  codec:
+    description: Holds subnode which indicates codec dai.
+    type: object
+    additionalProperties: false
+    properties:
+      sound-dai:
+        maxItems: 1
+    required:
+      - sound-dai
+
+required:
+  - compatible
+  - model
+  - mclk-fs
+  - cpu
+  - codec
+
+additionalProperties: false
+
+examples:
+  - |
+    sound {
+        compatible = "loongson,ls-audio-card";
+        model = "loongson-audio";
+        mclk-fs = <512>;
+
+        cpu {
+            sound-dai = <&i2s>;
+        };
+        codec {
+             sound-dai = <&es8323>;
+        };
+    };