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-4.9 'commit 973e6f5c37fc ("ARM: dts:
 msm: Add mem_dump node for msm8917")'.

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

Change-Id: I98d5bd60a047d6c5f1058faf67d0475e17d9fddc
Signed-off-by: Sudharsan Reddy Yettapu <syepattu@codeaurora.org>
Signed-off-by: Suresh Kumar Allam <allamsuresh@codeaurora.org>