m68k: merge the MMU and non-MMU versions of process.c

The MMU and non-MMU varients of the m68k arch process.c code are pretty
much the same. Only a few minor details differ between the two. The
majority of the difference is to deal with having or wanting hardware FPU
support. So merge them back into a single process.c file.

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