eventq: Major API change for the Event and EventQueue structures.

eventq: Major API change for the Event and EventQueue structures.

Since the early days of M5, an event needed to know which event queue
it was on, and that data was required at the time of construction of
the event object.  In the future parallelized M5, this sort of
requirement does not work well since the proper event queue will not
always be known at the time of construction of an event.  Now, events
are created, and the EventQueue itself has the schedule function,
e.g. eventq->schedule(event, when).  To simplify the syntax, I created
a class called EventManager which holds a pointer to an EventQueue and
provides the schedule interface that is a proxy for the EventQueue.
The intent is that objects that frequently schedule events can be
derived from EventManager and then they have the schedule interface.
SimObject and Port are examples of objects that will become
EventManagers.  The end result is that any SimObject can just call
schedule(event, when) and it will just call that SimObject's
eventq->schedule function.  Of course, some objects may have more than
one EventQueue, so this interface might not be perfect for those, but
they should be relatively few.