do all the magic dwc3 specific initalization as well
as reset the hub and power on the phys.
with this, "usb start" command is not needed anymore
from u-boot.
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.
