cpufreq: create a helper function to get CPU utilization

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
cpufreq: add generic get_cpuidle_time to the cpufreq headers so that we don't need to implement this everytime we need it.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
cpufreq: Introduce new relation for freq selection

Introduce CPUFREQ_RELATION_C for frequency selection.
It selects the frequency with the minimum euclidean distance
to target. In case of equal distance between 2 frequencies,
it will select the greater freq.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>