dt-bindings: display: msm: sm8450-mdss: document displayport controller subnode

Document the optional displayport controller subnode of the SM8450 MDSS.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/544000/
Link: https://lore.kernel.org/r/20230621-topic-sm8x50-upstream-mdss-bindings-dp-subnode-v2-2-733ed383f6b6@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Documentation/devicetree/bindings/display/msm/qcom,sm8450-mdss.yaml

@@ -42,6 +42,14 @@ patternProperties:
       compatible:
         const: qcom,sm8450-dpu
 
+  "^displayport-controller@[0-9a-f]+$":
+    type: object
+    properties:
+      compatible:
+        items:
+          - const: qcom,sm8450-dp
+          - const: qcom,sm8350-dp
+
   "^dsi@[0-9a-f]+$":
     type: object
     properties: