m68k: fix some atomic operation asm address modes for ColdFire

The ColdFire processors have a much more limited set of addressing modes
that can be used for most instructions. A number of the atomic operations
have already been fixed to limit the addressing modes used with add and
sub instructions when building for ColdFire. But we missed a few.
Fix the remaining atomic operations to be clean for ColdFire processors.

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