usb: gadget: Add snapshot of USB GSI function driver

This change adds USB GSI function driver which provides USB RMNET/RNDIS/
ECM/MBIM/DPL related functionalities with GSI hardware accelerated path.
This snapshot is taken as of msm-4.19 commit 104eef6e1fe8 ("platform:
msm: Remove unused local count variable").

This change also includes some fixups to match the modified API in
dwc3-msm.h.

Change-Id: If849fdeab445e99dc914060eae98e1948a48e3d2
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Jack Pham <jackp@codeaurora.org>