iwlwifi: trigger event log from debugfs

This patch adds a trigger for event log printing to debugfs.
It removes the triger from sysfs.

Signed-off-by: Ester Kummer <ester.kummer@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>