dt-bindings: display: mediatek: dp: Reference common DAI properties

The MediaTek DP hardware supports audio and exposes a DAI, so the
'#sound-dai-cells' property is needed for describing the DAI links.

Reference the dai-common.yaml schema to allow '#sound-dai-cells' to be
used, and filter out non-DP compatibles as MediaTek eDP in the same
binding doesn't support audio.

This fixes dtbs_check error:
'#sound-dai-cells' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Fei Shao <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://patchwork.kernel.org/project/dri-devel/patch/[e-mail]/
Signed-off-by: Chun-Kuang Hu <[e-mail]>

Documentation/devicetree/bindings/display/mediatek/mediatek,dp.yaml

···
   interrupts:
     maxItems: 1
 
+  '#sound-dai-cells':
+    const: 0
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports
     properties:
···
   - ports
   - max-linkrate-mhz
 
-additionalProperties: false
+allOf:
+  - $ref: /schemas/sound/dai-common.yaml#
+  - if:
+      not:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - mediatek,mt8188-dp-tx
+                - mediatek,mt8195-dp-tx
+    then:
+      properties:
+        '#sound-dai-cells': false
+
+unevaluatedProperties: false
 
 examples:
   - |