powerpc: VPHN topology change updates all siblings

When an associativity level change is found for one thread, the
siblings threads need to be updated as well.  This is done today
for PRRN in stage_topology_update() but is missing for VPHN in
update_cpu_associativity_changes_mask().

All threads should be updated to move to the new node.  Without this
patch, a single thread may be flagged for a topology change, leaving it
in a different node from its siblings, which is incorrect.  This causes
problems for the scheduler where overlapping scheduler groups are created
and a loop is formed in those groups.

Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>