Revert "PPC: pseries: Remove hack for PIO window"

This reverts commit a178274efabcbbc5d44805b51def874e47051325.

Contrary to that commit's message, the users of old_portio are not all
gone.  In particular VGA still uses it via portio_list_add().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
