m68knommu: add KMAP definitions for non-MMU definitions

To be consistent with the set of MMU definitions we should define KMAP_START
and KMAP_END. Future common m68k code will use their values.

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