sim: have a curTick per eventq

This patch adds a _curTick variable to an eventq. This variable is updated
whenever an event is serviced in function serviceOne(), or all events upto
a particular time are processed in function serviceEvents(). This change
helps when there are eventqs that do not make use of curTick for scheduling
events.

src/sim/simulate.cc

@@ -33,7 +33,7 @@
 #include "base/pollevent.hh"
 #include "base/types.hh"
 #include "sim/async.hh"
-#include "sim/eventq.hh"
+#include "sim/eventq_impl.hh"
 #include "sim/sim_events.hh"
 #include "sim/sim_exit.hh"
 #include "sim/simulate.hh"
@@ -65,9 +65,6 @@ simulate(Tick num_cycles)
         assert(curTick() <= mainEventQueue.nextTick() &&
                "event scheduled in the past");
 
-        // forward current cycle to the time of the first event on the
-        // queue
-        curTick(mainEventQueue.nextTick());
         Event *exit_event = mainEventQueue.serviceOne();
         if (exit_event != NULL) {
             // hit some kind of exit event; return to Python