usb: gadget: Introduce frame_number to usb_request

Add a field frame_number to the usb_request to report the interval
number in (micro)frames in which the isochronous transfer was
transmitted or received. The gadget driver can use this knowledge to
synchronize with the host. Also, this option is useful for debugging
purposes.

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>