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.

Change-Id: I61192a4065fddf567bcc97e066408135658fe46d
Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>