MINOR: cpu-topo: add a dump of thread-to-CPU mapping to -dc

MINOR: cpu-topo: add a dump of thread-to-CPU mapping to -dc

When emitting the CPU topology info with -dc, also emit a list of
thread-to-CPU mapping. The group/thread and thread ID are emitted
with the list of their CPUs on each line. The count of CPUs is shown
to ease comparisons, and as much as possible, we try to pack identical
lines within a group by showing thread ranges.