MINOR: cpu-topo: implement a sorting mechanism for CPU index

MINOR: cpu-topo: implement a sorting mechanism for CPU index

CPU selection will be performed by sorting CPUs according to
various criteria. For dumps however, that's really not convenient
and we'll need to reorder the CPUs according to their index only.
This is what the new function cpu_reorder_by_index() does. It's
called  in thread_detect_count() before dumping the CPU topology.