Add support for the XHCI function that is part of the Cadence USB3 DRD

Add support for the XHCI function that is part of the Cadence USB3 DRD
controller.  There are various incarnations of the controller.  This diff
only adds support for the "V1"/"CDNS3" version as found on the StarFive
JH7100 SoC.  Further changes may be needed to support controllers integrated
on other SoCs.

ok jsg@