m68k: fix io functions for ColdFire/MMU/PCI case

The inb/outb/... family of IO methods end up being multiply defined when
building PCI support for the ColdFire. Compiling gives this:

  CC      init/main.o
In file included from ./arch/m68k/include/asm/io.h:4:0,
                 from include/linux/bio.h:30,
                 from include/linux/blkdev.h:18,
                 from init/main.c:75:
./arch/m68k/include/asm/io_mm.h:420:0: warning: "inb" redefined
./arch/m68k/include/asm/io_mm.h:108:0: note: this is the location of the previous definition
...

The ColdFire/PCI case defines its own IO access methods, so no others
should be defined or used in this case. Conditionally disable other
definitions that clash with it.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>