iwlwifi: disable WoWLAN if !CONFIG_PM_SLEEP

If CONFIG_PM_SLEEP is disabled, then iwlwifi doesn't
support suspend/resume handlers and thus mac80211
(correctly) refuses advertising WoWLAN. Disable
WoWLAN in the driver in this case.

Cc: stable@kernel.org
Reported-by: Sebastian Kemper <sebastian_ml@gmx.net>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>