dt-bindings: gpu: arm,mali: restrict opp-table to objects

Simple 'opp-table:true' accepts a boolean property as opp-table, so
restrict it to object to properly enforce real OPP table nodes.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220818061713.9611-1-krzysztof.kozlowski@linaro.org

Documentation/devicetree/bindings/gpu/arm,mali-midgard.yaml

@@ -74,7 +74,8 @@ properties:
       - const: bus
 
   mali-supply: true
-  opp-table: true
+  opp-table:
+    type: object
 
   power-domains:
     maxItems: 1

Documentation/devicetree/bindings/gpu/arm,mali-utgard.yaml

@@ -101,7 +101,8 @@ properties:
 
   mali-supply: true
 
-  opp-table: true
+  opp-table:
+    type: object
 
   power-domains:
     maxItems: 1