usb: gadget: Add snapshot of USB RMNET Function driver

This change adds USB RMNET function driver which allows communication
between USB BAM and IPA BAM for RMNET and DPL functionalities over USB.

This snapshot is taken as of msm-4.4 'commit fa53f7f14b3c ("soc: qcom:
ipc_router_glink_xprt: Add rx intent timeout for glink")'.

This change adding changes to use cdev device instead of misc device
and also fixes different coding style related warnings.

Change-Id: I4c135765cd9a20fc512ae7e1970271275d8f1866
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>