cpupower: Introduce idle-set subcommand and C-state enabling/disabling

Example:

cpupower idle-set -d 3

will disable C-state 3 on all processors (set commands are active on
all CPUs by default), same as:

cpupower -c all idle-set -d 3

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>