numa: move default mapping init to machine

numa: move default mapping init to machine

there is no need use cpu_index_to_instance_props() for setting
default cpu -> node mapping. Generic machine code can do it
without cpu_index by just enabling already preset defaults
in possible_cpus.

PS:
as bonus it makes one less user of cpu_index_to_instance_props()

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1496161442-96665-3-git-send-email-imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>