tools/power turbostat: verify arguments to params --show and --hide

$ sudo turbostat --quiet --show junk
turbostat: Counter 'junk' can not be added.

Previously, invalid arguments to --show and --hide were silently ignored

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