cpuidle module implements cpuidle state discovery, query and
manipulation for a Linux device. This replaces the more primitive
get_cpuidle_states method of LinuxDevice.
Renamed APIs (and added a couple of new ones) to be more consistent:
"core" APIs take a core name as the parameter (e.g. "a15") or whatever
is listed in core_names for that device.
"cluster" APIs take a numeric cluster ID (eg. 0) as the parameter. These
get mapped using core_clusters for that device.
"cpu" APIs take a cpufreq cpu ID as a parameter. These could be
integers, e.g. 0, or full string id, e.g. "cpu0".
