spapr/kvm: Set default cpu model for all machine classes

spapr/kvm: Set default cpu model for all machine classes

We have to set the default model of all machine classes, not just for
the active one. Otherwise, "query-machines" will indicate the wrong
CPU model (e.g. "power9_v2.0-powerpc64-cpu" instead of
"host-powerpc64-cpu") as "default-cpu-type".

s390x already fixed this in de60a92e "s390x/kvm: Set default cpu model for
all machine classes".  This patch applies a similar fix for the pseries-*
machine types on ppc64.

Doing a
    {"execute":"query-machines"}
under KVM now results in
    {
      "hotpluggable-cpus": true,
      "name": "pseries-4.2",
      "numa-mem-supported": true,
      "default-cpu-type": "host-powerpc64-cpu",
      "is-default": true,
      "cpu-max": 1024,
      "deprecated": false,
      "alias": "pseries"
    },
    {
      "hotpluggable-cpus": true,
      "name": "pseries-4.1",
      "numa-mem-supported": true,
      "default-cpu-type": "host-powerpc64-cpu",
      "cpu-max": 1024,
      "deprecated": false
    },
    ...

Libvirt probes all machines via "-machine none,accel=kvm:tcg" and will
currently see the wrong CPU model under KVM.

Reported-by: Jiři Denemark <jdenemar@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>