musb: split out CPPI interrupt handler

As DaVinci DM646x has a dedicated CPPI DMA interrupt, replace
cppi_completion() (which has always been kind of layering
violation) by a complete CPPI interrupt handler.

[ dbrownell@users.sourceforge.net: only cppi_dma.c needs platform
device header, not cppi_dma.h ]

Signed-off-by: Dmitry Krivoschekov <dkrivoschekov@ru.mvista.com>
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>