If the host kernel lacks vfio DMA limit reporting, do not attempt
to shrink the guest DMA aperture.

Fixes: df202e3f ("s390x/pci: shrink DMA aperture to be bound by vfio DMA limit")
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Message-ID: <20231110175108.465851-3-mjrosato@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>