dt-bindings: usb: usb-device: make "compatible" optional

This binding was originally meant to describe hard-wired USB devices but
in some situations we need to describe USB ports. That is needed e.g. if
USB port is meant to be used as a trigger source but it can have any
device plugged. It's a common case for home routers which have USB ports
(with no hard-wired devices) and USB LEDs to indicate ports state.

There is no point (and no easy way) to add separate binding covering
just USB ports. Adjust existing devices binding to allow describing
ports.

This fixes:
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@21000: port@1: 'compatible' is a required property
        From schema: Documentation/devicetree/bindings/usb/generic-ehci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@21000: port@2: 'compatible' is a required property
        From schema: Documentation/devicetree/bindings/usb/generic-ehci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@21000: Unevaluated properties are not allowed ('#address-cells', '#size-cells', 'port@1', 'port@2' were unexpected)
        From schema: Documentation/devicetree/bindings/usb/generic-ehci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@22000: port@1: 'compatible' is a required property
        From schema: Documentation/devicetree/bindings/usb/generic-ohci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@22000: port@2: 'compatible' is a required property
        From schema: Documentation/devicetree/bindings/usb/generic-ohci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@22000: Unevaluated properties are not allowed ('#address-cells', '#size-cells', 'port@1', 'port@2' were unexpected)
        From schema: Documentation/devicetree/bindings/usb/generic-ohci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@23000: port@1: 'compatible' is a required property
        From schema: Documentation/devicetree/bindings/usb/generic-xhci.yaml
arch/arm/boot/dts/bcm4708-asus-rt-ac56u.dtb: usb@23000: Unevaluated properties are not allowed ('#address-cells', '#size-cells', 'phy-names', 'phys', 'port@1' were unexpected)
        From schema: Documentation/devicetree/bindings/usb/generic-xhci.yaml
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230228182909.1011-1-zajec5@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb-device.yaml

@@ -76,7 +76,6 @@ patternProperties:
         maxItems: 1
 
 required:
-  - compatible
   - reg
 
 additionalProperties: true