tools/power turbostat: Clear added counters when in no-msr mode

If user request --no-msr or is not able to access the MSRs,
turbostat should clear all the counters added with --add.
Because MSR access permission checks are done after the cmdline is
parsed, the decision has to be defered up until the transition into
no-msr mode happen.

Signed-off-by: Len Brown <len.brown@intel.com>