KVM: selftests: Guard struct kvm_vcpu_events with __KVM_HAVE_VCPU_EVENTS

The struct kvm_vcpu_events code is only available on certain architectures
(arm, arm64 and x86). To be able to compile kvm_util.c also for other
architectures, we have to fence the code with __KVM_HAVE_VCPU_EVENTS.

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190523164309.13345-3-thuth@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>