dt-bindings: display: advantech,idk-2121wr: reference common panel

Reference common panel bindings to bring descriptions of common fields
like panel-timing.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230823081107.82967-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/panel/advantech,idk-2121wr.yaml

@@ -19,6 +19,9 @@ description: |
   second port, therefore the ports must be marked accordingly (with either
   dual-lvds-odd-pixels or dual-lvds-even-pixels).
 
+allOf:
+  - $ref: panel-common.yaml#
+
 properties:
   compatible:
     items: