add_event_ex is added that takes an extra user_data pointer. This pointer is
passed to the callback (add_event and add_event_ex have slightly different
callbacks types). All callbacks also get the event id passed. Events added
with add_event_ex must be removed with remove_event_ex because the user_data
pointer must match in addition to the callback pointer.
On the other add_event is simplified to omit the oneshort parameter which
was almost always false (still there with add_event_ex).
As a side effect the ata_idle_notify callbacks are changed as well, they
do not take a data parameter anymore which was always NULL anyway.
This commit also adds some documentation to events.h
Change-Id: I13e29a0f88ef908f175b376d83550f9e0231f772
470989bd70