dt-bindings: gpu: add power-domains #cooling-cells to arm,mali-bifrost.yaml

A test with the command below gives this error:

arch/arm64/boot/dts/rockchip/px30-evb.dt.yaml: gpu@ff400000:
'#cooling-cells', 'power-domains'
do not match any of the regexes: 'pinctrl-[0-9]+'

With the conversion to yaml it also filters things
in a node that are used by other drivers like
'#cooling-cells' and 'power-domains'
for Rockchip px30 gpu nodes,
so add them to 'arm,mali-bifrost.yaml'.

make ARCH=arm64 dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/gpu/
arm,mali-bifrost.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>