m68k: merge MMU and non-MMU versions of mm/init.c

Some of the code in the existing mm/init_mm.c and mm/init_no.c files is
the same, and if we merge them back to a single file we can save some code
duplication.

Although the old mem_init() code for non-MMU was a little different than
the MMU version, it turns out we can use the same code. So I now we just
use the MMU mem_init() code for all. It also means we now get identical
console info messages for this code on kernel boot up.

So merge the two files back into a single file.

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