m68k/io: Move mem*io define guards to <asm/kmap.h>

The mem*io define guards are applicable to all users of <asm/kmap.h>.
Hence move them, and drop the #ifdef.

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