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-4.4 commit 4195f84bde61 ("qcom-charger:
smb2: add support of PMFALCON").

It removes usage of debug.h and related functionality used for debugging
purpose. IPC logging based debug functionality shall be added later.

Change-Id: Ia6915c76deb084ebb789ae33c509e835502cfcf1
Signed-off-by: Mayank Rana <mrana@codeaurora.org>