m68k: use mmu version of elf.h for non-mmu builds as well

Nothing specificly needed to support non-mmu m68k in elf.h,
so just use the mmu one.

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