xhci: Make sure xhci handles USB_SPEED_SUPER_PLUS devices.

BugLink: http://bugs.launchpad.net/bugs/1519623



In most cases the devices with the speed set to USB_SPEED_SUPER_PLUS
are handled like regular SuperSpeed devices.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 0caf6b33)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>