pc: disable pci-info

The BIOS that we ship in 1.7 does not use pci info
from host and so far isn't going to use it.
Taking in account problems it caused see 9604f70fdf and
to avoid future incompatibility issues, it's safest to
disable that interface by default for all machine types
including 1.7 as it was never exposed/used by guest.
And properly remove/cleanup it during 1.8 development cycle.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
