m68k: swtich non-mmu setups to use the mmu dma-mapping.h

The mmu version of dma-mapping.h (which is dma-mapping_mm.h) is clean
to be used for non-mmu setups as well. Remove dma-mapping_no.h and
revert dma-mapping_mm.h to dma-mapping.h

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>