This is mostly a copy of port/usbxhci.c with PCIWADDR() replaced
by PADDR() and the pci specific code stripped out.
This could be refactored at a later time.
There is a gpio line for the main hub reset that needs to be
asserted and some power management functions that are currently
done by u-boot (using "usb start" command).
We will do these ourselfs once we have the infrastructure for
it in place.
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