tools/power turbostat: Remove add_cstate_perf_counter_()

As the only caller of add_cstate_perf_counter_(),
add_cstate_perf_counter() just gives extra debug output on top. There is
no need to keep both functions.

Remove add_cstate_perf_counter_() and move all the logic to
add_cstate_perf_counter().

No functional change.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>