KVM: selftests: Verify disabling PMU virtualization via KVM_CAP_CONFIG_PMU

On a VM with PMU disabled via KVM_CAP_PMU_CONFIG, the PMU should not be
usable by the guest.

Signed-off-by: David Dunn <daviddunn@google.com>
Message-Id: <20220223225743.2703915-4-daviddunn@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>