Incomplete bus.h

[Martin Husemann <martin%duskware.de@localhost>]

Some m68k architectures have an incomplete bus.h header: it does not
define bus_dma_tag_t and friends. Solution would be to add a

 #include <m68k/bus_dma.h>

in there (as for example mac68k already does). This would fix -current
build failures in if_axe.c.

Is there any reason not to do this?

Martin

P.S.: currently failing m68k ports are: amiga, cesfic, hp300, luna68k, news68k
and sun3.