usb: define HCD_USB31 speed option for hosts that support USB 3.1 features

Hosts that support USB 3.1 Enhaned SuperSpeed can set their speed to
HCD_USB31 to let usb core and host drivers know that the controller
supports new USB 3.1 features.

make sure usb core handle HCD_USB31 hosts correctly, for now similar
to HCD_USB3.

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