tools/power turbostat: reduce debug output

A recent turbostat release increased topo.max_cpu_num
to make it convenient to handle sysfs bitmaps of 32-cpus.

But users, who regularly make use of "--debug", then saw a bunch of output
for cpus that were not present.

Remove that extra output by checking a cpu is online before dumping its info.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Prarit Bhargava <prarit@redhat.com>