thermal_mgmt: Add derivative term for PI controller
Created by: nicola-mazzucato-arm
The current implementation of Thermal Management provides a PI controller, without a derivative term.
Improve the controller by adding the derivative term, thus becoming a PID control.
At the same time, update the TC2 configuration as required by this change.
This change originates from: https://github.com/ARM-software/SCP-firmware/pull/856 and has been lightly reworked to improve readability, update unit testing and comply with coding style.
Change-Id: Ie0b667c680476714d4e6ad17afa3623ca36a56b8