tools/power turbostat: bug fixes to --add, --show/--hide features

Fix a bug with --add, where the title of the column
is un-initialized if not specified by the user.

The initial implementation of --show and --hide
neglected to handle the pc8/pc9/pc10 counters.

Fix a bug where "--show Core" only worked with --debug

Reported-by: Wendy Wang <wendy.wang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>