ASoC: dt-bindings: mediatek,mt7986-wm8960: add mt7986-wm8960 document

Add document for mt7986 board with wm8960.
Signed-off-by: Maso Huang <maso.huang@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230817101338.18782-6-maso.huang@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mediatek,mt7986-wm8960.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/mediatek,mt7986-wm8960.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek MT7986 sound card with WM8960 codec
+
+maintainers:
+  - Maso Huang <maso.huang@mediatek.com>
+
+allOf:
+  - $ref: sound-card-common.yaml#
+
+properties:
+  compatible:
+    const: mediatek,mt7986-wm8960-sound
+
+  platform:
+    type: object
+    additionalProperties: false
+    properties:
+      sound-dai:
+        description: The phandle of MT7986 platform.
+        maxItems: 1
+    required:
+      - sound-dai
+
+  codec:
+    type: object
+    additionalProperties: false
+    properties:
+      sound-dai:
+        description: The phandle of wm8960 codec.
+        maxItems: 1
+    required:
+      - sound-dai
+
+unevaluatedProperties: false
+
+required:
+  - compatible
+  - audio-routing
+  - platform
+  - codec
+
+examples:
+  - |
+    sound {
+        compatible = "mediatek,mt7986-wm8960-sound";
+        model = "mt7986-wm8960";
+        audio-routing =
+            "Headphone", "HP_L",
+            "Headphone", "HP_R",
+            "LINPUT1", "AMIC",
+            "RINPUT1", "AMIC";
+
+        platform {
+            sound-dai = <&afe>;
+        };
+
+        codec {
+            sound-dai = <&wm8960>;
+        };
+    };
+
+...