m68k: remove unused includes from dma.c

dma.c doesn't need most of the headers it includes.  Also there is
no point in undefining the DEBUG symbol given that it isn't used
anywhere in this small file.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Greg Ungerer <gerg@linux-m68k.org>