xenpm: add cpu frequency control interface, through which user can

xenpm: add cpu frequency control interface, through which user can
tune the parameters manually.

Now, xenpm can be invoked with the following options:
Usage:
       xenpm get-cpuidle-states [cpuid]: list cpu idle information on
       CPU cpuid or all CPUs.
       xenpm get-cpufreq-states [cpuid]: list cpu frequency
       information on CPU cpuid or all CPUs.
       xenpm get-cpufreq-para [cpuid]: list cpu frequency information
       on CPU cpuid or all CPUs.
       xenpm set-scaling-maxfreq <cpuid> <HZ>: set max cpu frequency
       <HZ> on CPU <cpuid>.
       xenpm set-scaling-minfreq <cpuid> <HZ>: set min cpu frequency
       <HZ> on CPU <cpuid>.
       xenpm set-scaling-governor <cpuid> <name>: set scaling governor
       on CPU <cpuid>.
       xenpm set-scaling-speed <cpuid> <num>: set scaling speed on CPU
       <cpuid>.
       xenpm set-sampling-rate <cpuid> <num>: set sampling rate on CPU
       <cpuid>.
       xenpm set-up-threshold <cpuid> <num>: set up threshold on CPU
       <cpuid>.

To ease the use of this tool, the shortcut option is supported,
i.e. `xenpm get-cpui' is equal to `xenpm get-cpuidle-states'.

Signed-off-by: Guanqun Lu <guanqun.lu@intel.com>