usb: Add USB 3.1 SuperSpeedPlus device capability descriptor

USB 3.1 SuperSpeedPlus device capability descriptor is returned as part
of the bos descriptor for devices that support SuperSpeedPlus protocol.

The descriptor contains more detailed information about the supported
speeds of the device. More details about the descriptor can be found in
the USB 3.1 specification section 9.6.2.5

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