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>

Documentation/devicetree/bindings/usb/dwc2.yaml

@@ -78,6 +78,9 @@ properties:
   phy-names:
     const: usb2-phy
 
+  power-domains:
+    maxItems: 1
+
   vbus-supply:
     description: reference to the VBUS regulator. Depending on the current mode
       this is enabled (in "host" mode") or disabled (in "peripheral" mode). The