tlp-usblist: print <unknown> if device $desc is empty

Signed-off-by: Thomas Koch <linrunner@gmx.net>
tlp-stat: do not set needs_root_priv=0 directly

in read_args(): do not set needs_root_priv=0 if it has already been set.
This fixes execution of tlp-stat with the --battery arg followed by any
other arg that sets needs_root_priv to 0.

Signed-off-by: Thomas Koch <linrunner@gmx.net>
Enable/Disable dynamic overclocking

This commit adds support for disabling/allowing dynamic overclocking ("Intel
Turbo Boost", "AMD Turbo-Core") depending on the power state.
This is controlled via the CPU_BOOST_ON_AC/CPU_BOOST_ON_BAT config option;
a value of '0' disables boosting while '1' allows it. The default behavior is
not to control boosting.

Same objections as for cpufreq governor control apply:
* peak performance decreases
* high power consumption for a short duration vs. low..moderate power consump-
  tion for a longer duration (generally speaking)
  * feature may conflict with the distribution's cpufreq settings

  Reasons why boost control could be useful:
  * do not exceed power/temperature limits while on battery mode,
    even if only for a short duration
    * (also see the respective kernel commit, "Add support for disabling dynamic
      overclocking", ref 615b7300717b9ad5c23d1f391843484fe30f6c12

Note that this feature requires a recent kernel (linux 3.7 and later).

Signed-off-by: Thomas Koch <linrunner@gmx.net>
Dynamic overclocking feature:
- simplify config comments
- update copyright
- update changelog
tlp-stat: show turbo boost