drivers/thermal/devfreq_cooling: Use new Energy Model interface

Energy Model framework support modifications at runtime of the power
values. Use the new EM table which is protected with RCU. Align the
code so that this RCU read section is short.

This change is not expected to alter the general functionality.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>