xhci: debugfs: add usb ports to xhci debugfs

Add ports/portxx/portsc for each xHC hardware usb port to debugfs.
Showing the content of the port status and control register for
each port (PORTSC)

Portxx is numbered starting from 1 for historical reasons to better
match port numbering shown by lsusb and other places.

Ports in debugfs are in the order XHC controller has them,
In most cases USB2 ports come first, followed by USB3 ports.
i.e. USB2 ports are port01-portxx, and USB3 portxx-portmax.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>