USB: Rename "msm72k_otg.c" to "msm_otg.c"

This driver is used across all MSM SoCs.  Hence give a generic name.
All Functions and strutures are also using "msm_otg" as prefix.

Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>