tools/power turbostat: support "--hide C1" etc.

Originally, the only way to hide the sysfs C-state statistics columns
was with "--hide sysfs".  This was because we process "--hide" before
we probe for those columns.

hack --hide to remember deferred hide requests, and apply
them when sysfs is probed.

"--hide sysfs" is still available as short-hand to refer to
the entire group of counters.

The down-side of this change is that we no longer error check for
bogus --hide column names.  But the user will quickly figure that
out if a column they mean to hide is still there...

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