ArmPkg/TimerDxe: remove workaround for KVM timer handling

When we first ported EDK2 to KVM/arm, we implemented a workaround for
the quirky timer handling on the KVM side. This has been fixed in
Linux commit f120cd6533d2 ("KVM: arm/arm64: timer: Allow the timer to
control the active state") dated 23 June 2014, which was incorporated
into Linux release 4.3.

So almost 4 years later, it should be safe to drop this workaround on
the EDK2 side.

This reverts commit b1a633434d.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

ArmPkg/Drivers/TimerDxe/TimerDxe.c

@@ -337,7 +337,6 @@ TimerInterruptHandler (
 
     // Set next compare value
     ArmGenericTimerSetCompareVal (CompareValue);
-    ArmGenericTimerEnableTimer ();
     ArmInstructionSynchronizationBarrier ();
   }
 

ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c

@@ -26,16 +26,6 @@ ArmGenericTimerEnableTimer (
 
   TimerCtrlReg = ArmReadCntvCtl ();
   TimerCtrlReg |= ARM_ARCH_TIMER_ENABLE;
-
-  //
-  // When running under KVM, we need to unmask the interrupt on the timer side
-  // as KVM will mask it when servicing the interrupt at the hypervisor level
-  // and delivering the virtual timer interrupt to the guest. Otherwise, the
-  // interrupt will fire again, trapping into the hypervisor again, etc. etc.
-  // This is scheduled to be fixed on the KVM side, but there is no harm in
-  // leaving this in once KVM gets fixed.
-  //
-  TimerCtrlReg &= ~ARM_ARCH_TIMER_IMASK;
   ArmWriteCntvCtl (TimerCtrlReg);
 }