thermal: convert rcar_thermal to use devm_thermal_zone_of_sensor_register

This changes the driver to use the devm_ version
of thermal_zone_of_sensor_register and cleans
up the  local points and unregister calls.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>