thermal: fix Mediatek thermal controller build

At least with CONFIG_COMPILE_TEST, there's no reason to assume
that CONFIG_RESET_CONTROLLER is set, but the code for this
controller requires it since it calls device_reset().

Make CONFIG_MTK_THERMAL properly depend on CONFIG_RESET_CONTROLLER.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>