ata_piix: Turn on hotplugging support for older chips

We can't do this for the later ones as they have all sorts of magic boot
time stuff that needs reviewing and the like. However we can do it for the
older ones and it turns out we need to as some IBM docking stations have a
second PIIX series device in them and without this change you can't use it
very well

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>