thermal/core: Fix missing stub for devm_thermal_cooling_device_register

thermal/core: Fix missing stub for devm_thermal_cooling_device_register

Even it is very unlikely the thermal framework is disabled, the newly
added devm_thermal_cooling_device_register() function has not the stub
when the thermal framework is optout in the kernel.

Add it.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605301554.S9n45bfQ-lkp@intel.com/
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Link: https://patch.msgid.link/20260601090152.1243983-2-daniel.lezcano@kernel.org