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/mem/packet_queue.cc

@@ -41,6 +41,7 @@
  *          Andreas Hansson
  */
 
+#include "base/trace.hh"
 #include "debug/Drain.hh"
 #include "debug/PacketQueue.hh"
 #include "mem/packet_queue.hh"