dt-bindings: display/msm: dp-controller: allow eDP for SA8775P

On Qualcomm SA8775P the DP controller might be driving either a
DisplayPort or a eDP sink (depending on the PHY that is tied to the
controller). Reflect that in the schema.

Acked-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/672569/
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/display/msm/dp-controller.yaml

···
       properties:
         "#sound-dai-cells": false
     else:
-      properties:
-        aux-bus: false
-        reg:
-          minItems: 5
-      required:
-        - "#sound-dai-cells"
+      if:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - qcom,sa8775p-dp
+      then:
+        oneOf:
+          - required:
+              - aux-bus
+          - required:
+              - "#sound-dai-cells"
+      else:
+        properties:
+          aux-bus: false
+          reg:
+            minItems: 5
+        required:
+          - "#sound-dai-cells"
 
 additionalProperties: false