arch_topology: Set thread sibling cpumask only within the cluster

Currently the cluster identifier is not set on the DT based platforms.
The reset or default value is -1 for all the CPUs. Once we assign the
cluster identifier values correctly that may result in getting the thread
siblings wrong as the core identifiers can be same for 2 different CPUs
belonging to 2 different cluster.

So, in order to get the thread sibling cpumasks correct, we need to
update them only if the cores they belong are in the same cluster within
the socket. Let us skip updation of the thread sibling cpumaks if the
cluster identifier doesn't match.

This change won't affect even if the cluster identifiers are not set
currently but will avoid any breakage once we set the same correctly.

Tested-by: Gavin Shan <gshan@redhat.com>
Tested-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>