memory: crack wide ioport accesses into smaller ones when needed

The memory API supports cracking wide accesses into narrower ones
when needed; but this was no implemented for the pio address space,
causing lsi53c895a's IO BAR to malfunction.

Fix by correctly cracking wide accesses when needed.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>