usb: dwc3: gadget: Report isoc transfer frame number

Implement the new frame_number API to report the isochronous interval
frame number. This patch checks and reports the interval in which the
isoc transfer was transmitted or received via the Isoc-First TRB SOF
number field.

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