m68k/m68knommu: merge machdep.h files into a single file

No need to have separate machdep.h files for each of the MMU and non-MMU
cases. Merge them all into a single file.

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