xhci: parse xhci protocol speed ID list for usb 3.1 usage

xhci 1.1 controllers that support USB 3.1 must provide a protocol speed ID
(PSI) list to inform the driver of the supported speeds.

The PSI list can be read from the xhci supported protocol extended
capabilities.
The PSI values will be used to create a USB 3.1 SuperSpeedPlus capability
descriptor for the xhci USB 3.1 roothub.

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