msm: usb_bam: move private definitions to usb_bam.c

Several structure and enum declarations are only used within
the implementation code in usb_bam.c, and do not need to be
exposed in the public header. Move them. Also, clean up the
included headers in usb_bam.h to only the minimal required ones.

Change-Id: Iaade580bd2fa9c50da0e9b2288fc3aeb3d98b2d4
Signed-off-by: Jack Pham <jackp@codeaurora.org>