dt-bindings: usb: dwc3: Add IPQ9574 compatible

* Document the IPQ9574 dwc3 compatible.

* Make power-domains as optional since IPQ9574 doesn't have GDSCs

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.com>
Link: https://lore.kernel.org/r/27fc578e549e12a4d689cdd434107964b529c4f4.1686289721.git.quic_varada@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>