dt-bindings: usb: dwc2: add power-domains property

A test with the command below gives this error:

arch/arm64/boot/dts/rockchip/px30-evb.dt.yaml: usb@ff300000:
'power-domains' does 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
'power-domains' for Rockchip px30 usb nodes,
so add them to 'dwc2.yaml'.

make ARCH=arm64 dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/usb/dwc2.yaml

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