dt-bindings: display/msm/gmu: Allow passing QMP handle

When booting the GMU, the QMP mailbox should be pinged about some tunables
(e.g. adaptive clock distribution state). To achieve that, a reference to
it is necessary. Allow it and require it with A730.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # sm8450
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/559279/
Signed-off-by: Rob Clark <robdclark@chromium.org>

Documentation/devicetree/bindings/display/msm/gmu.yaml

@@ -64,6 +64,10 @@ properties:
   iommus:
     maxItems: 1
 
+  qcom,qmp:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description: Reference to the AOSS side-channel message RAM
+
   operating-points-v2: true
 
   opp-table:
@@ -251,6 +255,9 @@ allOf:
             - const: hub
             - const: demet
 
+      required:
+        - qcom,qmp
+
   - if:
       properties:
         compatible: