spapr: Allow only supported dynamic sysbus devices

spapr: Allow only supported dynamic sysbus devices

TYPE_SPAPR_PCI_HOST_BRIDGE is the only dynamic sysbus device not
rejected by ppc_spapr_reset(), so it can be the only entry on the
allowed list.

Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Alexander Graf <agraf@suse.de>
Cc: qemu-ppc@nongnu.org
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20171125151610.20547-5-ehabkost@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>