dt-bindings: gpu: vivante,gc: Add common properties

Add common properties appearing in DTSes (cooling-cells, assigned-clocks
and others) to fix dtbs_check warnings like:

  arch/arm64/boot/dts/freescale/imx8mq-evk.dt.yaml: gpu@38000000:
    '#cooling-cells', 'assigned-clock-parents', 'assigned-clock-rates', 'assigned-clocks' do not match any of the regexes: 'pinctrl-[0-9]+'

Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200904145312.10960-5-krzk@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/gpu/vivante,gc.yaml

@@ -21,6 +21,13 @@ properties:
   interrupts:
     maxItems: 1
 
+  '#cooling-cells':
+    const: 2
+
+  assigned-clock-parents: true
+  assigned-clock-rates: true
+  assigned-clocks: true
+
   clocks:
     items:
       - description: AXI/master interface clock