Also remove board-omap3beagle.h that is not included anywhere,
and move protoype for voiceblue_reset() from board-voiceblue.h
to system.h.

After this patch there are still board-ams-delta.h, board-sx1.h
and board-voiceblue.h that export some functions. These could
be removed if the functions were moved under drivers.
Signed-off-by: Tony Lindgren <tony@atomide.com>