usb: dwc3: gadget: set PCM1 field of isochronous-first TRBs

In case of High-Speed, High-Bandwidth endpoints, we
need to tell DWC3 that we have more than one packet
per interval. We do that by setting PCM1 field of
Isochronous-First TRB.

Cc: <stable@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>