m68k: move *_relaxed macros into io_no.h and io_mm.h

Move a copy of the definitions of the *_relaxed() macros into io_no.h
and io_mm.h. This precedes a change to the io_no.h file to use
asm-generic/io.h. They will be removed from io_no.h at that point.

Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Angelo Dureghello <angelo@sysam.it>
Tested-by: Angelo Dureghello <angelo@sysam.it>