cpu: Correctly call parent on switchOut() and takeOverFrom()

This patch cleans up the CPU switching functionality by making sure
that CPU models consistently call the parent on switchOut() and
takeOverFrom(). This has the following implications that might alter
current functionality:

 * The call to BaseCPU::switchout() in the O3 CPU is moved from
   signalDrained() (!) to switchOut().

 * A call to BaseSimpleCPU::switchOut() is introduced in the simple
   CPUs.

src/cpu/o3/cpu.cc

@@ -1192,8 +1192,6 @@ FullO3CPU<Impl>::signalDrained()
 
         setDrainState(Drainable::Drained);
 
-        BaseCPU::switchOut();
-
         if (drainManager) {
             DPRINTF(Drain, "CPU done draining, processing drain event\n");
             drainManager->signalDrainDone();
@@ -1207,6 +1205,8 @@ template <class Impl>
 void
 FullO3CPU<Impl>::switchOut()
 {
+    BaseCPU::switchOut();
+
     fetch.switchOut();
     rename.switchOut();
     iew.switchOut();

src/cpu/simple/atomic.cc

@@ -177,6 +177,8 @@ AtomicSimpleCPU::drainResume()
 void
 AtomicSimpleCPU::switchOut()
 {
+    BaseSimpleCPU::switchOut();
+
     assert(_status == BaseSimpleCPU::Running || _status == Idle);
     _status = SwitchedOut;
 
@@ -187,7 +189,7 @@ AtomicSimpleCPU::switchOut()
 void
 AtomicSimpleCPU::takeOverFrom(BaseCPU *oldCPU)
 {
-    BaseCPU::takeOverFrom(oldCPU);
+    BaseSimpleCPU::takeOverFrom(oldCPU);
 
     assert(!tickEvent.scheduled());
 

src/cpu/simple/timing.cc

@@ -163,6 +163,8 @@ TimingSimpleCPU::drainResume()
 void
 TimingSimpleCPU::switchOut()
 {
+    BaseSimpleCPU::switchOut();
+
     assert(_status == BaseSimpleCPU::Running || _status == Idle);
     _status = SwitchedOut;
     numCycles += curCycle() - previousCycle;
@@ -177,7 +179,7 @@ TimingSimpleCPU::switchOut()
 void
 TimingSimpleCPU::takeOverFrom(BaseCPU *oldCPU)
 {
-    BaseCPU::takeOverFrom(oldCPU);
+    BaseSimpleCPU::takeOverFrom(oldCPU);
 
     // if any of this CPU's ThreadContexts are active, mark the CPU as
     // running and schedule its tick event.