cpupower: Add cpuidle parts into library

This more or less is a renaming and moving of functions and should not
introduce any functional change.

cpupower was built from cpufrequtils (which had a C library providing easy
access to cpu frequency platform info). In the meantime it got enhanced
by quite some neat cpuidle userspace tools.

Now the cpu idle functions have been separated and added to the cpupower.so
library.
So beside an already existing public header file:
cpufreq.h
cpupower now also exports these cpu idle functions in:
cpuidle.h

Here again pasted for better review of the interfaces:

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int cpuidle_is_state_disabled(unsigned int cpu,
                                       unsigned int idlestate);
int cpuidle_state_disable(unsigned int cpu, unsigned int idlestate,
                                   unsigned int disable);
unsigned long cpuidle_state_latency(unsigned int cpu,
                                                unsigned int idlestate);
unsigned long cpuidle_state_usage(unsigned int cpu,
                                        unsigned int idlestate);
unsigned long long cpuidle_state_time(unsigned int cpu,
                                                unsigned int idlestate);
char *cpuidle_state_name(unsigned int cpu,
                                unsigned int idlestate);
char *cpuidle_state_desc(unsigned int cpu,
                                unsigned int idlestate);
unsigned int cpuidle_state_count(unsigned int cpu);

char *cpuidle_get_governor(void);
char *cpuidle_get_driver(void);

======================================

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