usb: dwc3: Add snapshot of DWC3 MSM drivers

This change adds dwc3-msm.c and dbm.c which together form
the driver for the USB controller on QTI MSM devices. Also
included are the Makefile, Kconfig, and supporting devicetree
bindings documentation. This snapshot is taken as of msm-4.14
commit <a9cdbef84b97de> ("Merge "usb: phy: Enable proper DP DM
masks for PHY interrupts""). The files have been slightly modified
to correct minor checkpatch style warnings.

Change-Id: I9a13cb5bae2f5c1e98906d1cb52134c2dea0bc80
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>