usb: dwc3: gadget: Handle XferComplete for streams

In DWC3, to prepare TRBs for streams, all the TRBs of a transfer will
use the same stream ID. To start a new stream, the driver needs to wait
for the current transfer to complete or ended (by END_TRANFER command).
As a result, inform the controller of the last TRB of a transfer so that
it knows when a transfer completes and start a new transfer of a new
stream.

Even though the transfer completion handling can be applied for other
non-isoc endpoints, only do it for streams due to its requirement.
It's better to keep the controller's TRB cache full than waiting for
transfer completion and starting a new transfer.

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>