vfio doesn't support guest iommus yet, indicate it to the user
by gently depositing a core on their disk.
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAvi Kivity <avi.kivity@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>