usb: dwc3: msm: Move dwc3_otg to dwc3-msm

The dwc3_otg driver was originally intended to be a generic OTG
layer for the DWC3 core, but the reality is that it is highly
coupled with the MSM-specific implementation. Also, since the
HW-based OTG implementation is not used anymore, in the end its
only useful purpose is to handle role-switching between host
and peripheral modes, which can be done much more simply if
handled directly in the MSM glue.
This patch moves the contents of the dwc3_otg.c file
verbatim to dwc3-msm.c. Follow-up patches will consolidate
redundant structures and eventually remove dwc3_otg.h.

Change-Id: Ib28868fb49d00072d72349c85645450b1af334aa
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>