MINOR: cpu-topo: create an array of the clusters

MINOR: cpu-topo: create an array of the clusters

The goal here is to keep an array of the known CPU clusters, because
we'll use that often to decide of the performance of a cluster and
its relevance compared to other ones. We'll store the number of CPUs
in it, the total capacity etc. For the capacity, we count one unit
per core, and 1/3 of it per extra SMT thread, since this is roughly
what has been measured on modern CPUs.

In order to ease debugging, they're also dumped with -dc.