cpufreq-dt: Supply power coefficient when registering cooling devices

Support registering cooling devices with dynamic power coefficient
where provided by the device tree. This allows OF registered cooling
devices driver to be used with the power_allocator thermal governor.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit f8fa8ae06b8c2c25d81c99766f9226adc5c3e073)
Signed-off-by: Alex Shi <alex.shi@linaro.org>