qemu: mdev: Use vfio-pci 'display' property only with vfio-pci mdevs

S390 is aware of both vfio-pci and vfio-ccw devices, so
on S390 the capability QEMU_CAPS_VFIO_PCI_DISPLAY will be
available. Add an extra check to make sure we only set the
display to off for vfio-pci mediated devices. Otherwise we
add display for vfio-ccw device and this breaks vfio-ccw
device qemu command line.

Fixes: d54e45b6 conf: Introduce new <hostdev> attribute 'display'
Signed-off-by: NFarhan Ali <alifm@linux.ibm.com>
Reviewed-by: NMarc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/qemu/qemu_domain.c

@@ -6391,6 +6391,7 @@ qemuDomainHostdevDefMdevPostParse(virDomainHostdevSubsysMediatedDevPtr mdevsrc,
     /* QEMU 2.12 added support for vfio-pci display type, we default to
      * 'display=off' to stay safe from future changes */
     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_VFIO_PCI_DISPLAY) &&
+        mdevsrc->model == VIR_MDEV_MODEL_TYPE_VFIO_PCI &&
         mdevsrc->display == VIR_TRISTATE_SWITCH_ABSENT)
         mdevsrc->display = VIR_TRISTATE_SWITCH_OFF;