Missing 'clocks' on most nodes with 'compatible = "nxp,kinetis-usbd"'

[ulfalizer]

dts/bindings/usb/nxp,kinetis-usbd.yaml says that any node with that binding must have a clocks property, but only a few nodes with compatible = "nxp,kinetis-usbd" have a clocks property.

List for reference:

$ git grep nxp,kinetis-usbd
boards/arm/frdm_k64f/frdm_k64f.dts:     compatible = "nxp,kinetis-usbd";
boards/arm/frdm_kl25z/frdm_kl25z.dts:   compatible = "nxp,kinetis-usbd";
boards/arm/usb_kw24d512/usb_kw24d512.dts:       compatible = "nxp,kinetis-usbd";
dts/arm/nxp/nxp_k6x.dtsi:                       compatible = "nxp,kinetis-usbd";
dts/arm/nxp/nxp_kl25z.dtsi:                     compatible = "nxp,kinetis-usbd";
dts/arm/nxp/nxp_kw2xd.dtsi:                     compatible = "nxp,kinetis-usbd";
dts/arm/nxp/nxp_rt.dtsi:                        compatible = "nxp,kinetis-usbd";
dts/arm/nxp/nxp_rt.dtsi:                        compatible = "nxp,kinetis-usbd";
dts/bindings/usb/nxp,kinetis-usbd.yaml:      constraint: "nxp,kinetis-usbd"

This leads to failures in #17660, which turns missing category: required properties into an error.

Not familiar enough with how this is used to know what the proper solution is. A quickfix would be to make clocks optional instead in the binding (category: optional).

[ulfalizer]

CC @pizi-nordic @jfischer-phytec-iot @galak

[pizi-nordic]

It looks that I forgot cleaning this out while refactoring #16957 N-th time. I will create PR which will make the clocks optional.