iwlwifi: LED cleanup

The iwlwifi drivers have LED blinking requirements that
mac80211 cannot fulfill due to the use of just a single
LED instead of different ones for TX, RX, radio etc.
Instead, the single LED blinks according to transfers
and is solid on the rest of the time. As such, having
LED class devices registered that mac80211 triggers are
connected to is pointless as we don't use the triggers
anyway.

Remove all the useless code and add hooks into the
driver itself. At the same time, make the LED code
abstracted so the core code that determines blink rate
etc. can be shared between 3945 and agn in iwlcore.

At the same time, the fact that we removed the use of
the mac80211 LED triggers means we can also remove the
IWLWIFI_LEDS Kconfig symbol since the LED support is
now self-contained.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>