cpu_cooling: Make of_cpufreq_power_cooling_register() parse DT

All the callers of of_cpufreq_power_cooling_register() have almost
identical code and it makes more sense to move that code into the helper
as its all about reading DT properties.

This got rid of lot of redundant code.

Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>