dt-bindings: gpu: mali-utgard: Add the #cooling-cells property

The GPU can be one of the big heat sources on a SoC. Allow the
"#cooling-cells" property to be specified for ARM Mali Utgard GPUs so
the GPU clock speeds (and voltages) can be reduced to prevent a SoC from
overheating.
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>

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

@@ -107,6 +107,9 @@ properties:
 
   operating-points-v2: true
 
+  "#cooling-cells":
+    const: 2
+
 required:
   - compatible
   - reg
@@ -164,6 +167,7 @@ examples:
       clocks = <&ccu 1>, <&ccu 2>;
       clock-names = "bus", "core";
       resets = <&ccu 1>;
+      #cooling-cells = <2>;
     };
 
 ...