usb: dwc3: gadget: track number of TRBs per request

commit 09fe1f8d7e2f461275b1cdd832f2cfa5e9be346d upstream

This will help us remove the wait_event() from our ->dequeue().

Cc: Fei Yang <fei.yang@intel.com>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: linux-usb@vger.kernel.org
Cc: stable@vger.kernel.org # 4.19.y
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
(cherry picked from commit 09fe1f8d7e2f461275b1cdd832f2cfa5e9be346d)
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>