xhci: add port speed ID to portsc tracing

Shows the port speed protocol speed ID (PSID) in use.
speed ID may map to custom speeds, but in most cases it uses default

1 = Full-Speed        12 MB/s
2 = Low-Speed         1.5 Mb/s
3 = High-speed        480 Mb/s
4 = SuperSpeed        5 Gb/s
5 = SuperSpeedPlus    10 Gb/s

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