Just specifying ops = NULL in some cases can be more convenient than having
two functions.

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 78a379ab1b6b30ab497db7971ad336dad1dbee76.1438758065.git.p.fedin@samsung.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>