numa: consolidate cpu_preplug fixups/checks for pc/arm/spapr

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <1496161442-96665-2-git-send-email-imammedo@redhat.com>
[ehabkost: Fix indentation]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
