io mapping: clean up #ifdefs

Impact: cleanup

clean up ifdefs: change #ifdef CONFIG_X86_32/64 to
CONFIG_HAVE_ATOMIC_IOMAP.

flip around the #ifdef sections to clean up the structure.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>