iwlwifi: make LED support optional

If there's no LED on the system, it doesn't make a lot of sense
to include close to 4k of LED-related code (mostly in mac80211),
so instead of forcing LED support into the kernel, don't build
iwlwifi/mac80211 LED support if there's no LED class support.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: EliadX Peller <eliad@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>