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/root.cc

@@ -32,6 +32,7 @@
  */
 
 #include "base/misc.hh"
+#include "base/trace.hh"
 #include "config/the_isa.hh"
 #include "debug/TimeSync.hh"
 #include "sim/full_system.hh"