dev-arm: Set cntkctl and cnthctl in the CoreTimers constructor.

The cntkctl and cnthctl registers were not initialized by the CoreTimers
constructor which upset valgrind when they were later used by
handleStream.

Change-Id: Iaedbb2d957aeb428fd563be2e24ccb8d2cf57f26
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52403
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/dev/arm/generic_timer.cc

@@ -730,6 +730,7 @@ GenericTimer::CoreTimers::CoreTimers(GenericTimer &_parent,
     ArmInterruptPin *_irqVirt, ArmInterruptPin *_irqHyp)
       : parent(_parent),
         cntfrq(parent.params().cntfrq),
+        cntkctl(0), cnthctl(0),
         threadContext(system.threads[cpu]),
         irqPhysS(_irqPhysS),
         irqPhysNS(_irqPhysNS),