numa: use possible_cpus for not mapped CPUs check

and remove corresponding part in numa.c that uses
node_cpu bitmaps.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-Id: <1494415802-227633-16-git-send-email-imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
