iwlwifi: mvm: refactor temperature notification handling

Refactor the temperature handling code so that it is easier to reuse
it with other notification flows.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>