usb: misc: usbtest: add super-speed isoc support

The calculation of packet number within microframe is different between
high-speed and super-speed endpoint, we add support for super-speed
in this patch.

Cc: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>