iwlwifi: use mac80211 throughput trigger

Instead of keeping track of LED blink speed
in the driver, use the new mac80211 trigger
and link it up with an LED classdev that we
now register. This also allows users more
flexibility in how they want to have the LED
blink or not.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>