dt-bindings: display/msm: dpu-sdm845: add missing DPU opp-table

The 'display-controller' child (DPU) of Display SubSystem (MDSS) uses
opp-table, so reference it which allows restricting DPU schema to fixed
list of properties.

Fixes: 3d7a0dd8f39b ("dt-bindings: msm: disp: add yaml schemas for DPU bindings")
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/499212/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>
Signed-off-by: Rob Clark <[e-mail]>

Documentation/devicetree/bindings/display/msm/dpu-sdm845.yaml

···
   "^display-controller@[0-9a-f]+$":
     type: object
     description: Node containing the properties of DPU.
+    additionalProperties: false
 
     properties:
       compatible:
···
         maxItems: 1
 
       operating-points-v2: true
+      opp-table:
+        type: object
+
       ports:
         $ref: /schemas/graph.yaml#/properties/ports
         description: |