usb: musb: allow board to pass down fifo mode

boards might want to optimize their fifo configuration
to the particular needs of that specific board. Allow
that by moving all related data structures to
<linux/usb/musb.h>

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>