spapr: ensure that all threads within core are on the same NUMA node

Threads within a core shouldn't be on different
NUMA nodes, so if user has misconfgured command
line, fail QEMU at start up to force user fix it.

For now use the first thread on the core as source
of core's node-id. Later when cpu-numa refactoring
lands  it will be switched to core's node-id from
possible_cpus[].

This prevents the same problems as commit 20bb648d
"spapr: Fix default NUMA node allocation for threads",
but for the case of manually configured NUMA node
mappings, instead of just the default case.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
