tools/power/x86/intel-speed-select: Allow display non-cpu power domain info

Some power domain may not have CPUs associated, allow displaying
information for these non-cpu power domains.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>