KVM: arm/arm64: arch_timer: Simplify kvm_timer_vcpu_terminate

KVM: arm/arm64: arch_timer: Simplify kvm_timer_vcpu_terminate

kvm_timer_vcpu_terminate can only be called in two scenarios:

 1. As part of cleanup during a failed VCPU create
 2. As part of freeing the whole VM (struct kvm refcount == 0)

In the first case, we cannot have programmed any timers or mapped any
IRQs, and therefore we do not have to cancel anything or unmap anything.

In the second case, the VCPU will have gone through kvm_timer_vcpu_put,
which will have canceled the emulated physical timer's hrtimer, and we
do not need to that here as well.  We also do not care if the irq is
recorded as mapped or not in the VGIC data structure, because the whole
VM is going away.  That leaves us only with having to ensure that we
cancel the bg_timer if we were blocking the last time we called
kvm_timer_vcpu_put().

Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>