iwlwifi: device tracing

In order to have an easier way to debug issues, create
trace events (using the ftrace framework) that will
allow us to follow exactly what the driver is doing
with the device.

The text format isn't all that useful, but the binary
format can also be obtained easily via debugfs and
then analysed on the fly or offline with debugging
tools.

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>