musb_hdrc cleanup -- cppi and sparse

Cleanup for CPPI DMA (for DaVinci, and someday TUSB6020):

 - Move state ram structs to CPPI header, it's not DaVinci-specific

 - Do some associated CamelCase removal, in conjunction with removing
   inappropriate "volatile" declarations.

This resolves a bunch of "sparse" warnings with this code, most of which
seem to have been caused by bugs in older versions of "sparse".

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>