q35: Allow only supported dynamic sysbus devices

The only user-creatable sysbus devices in qemu-system-x86_64 are
amd-iommu, intel-iommu, and xen-backend.  xen-backend is handled
by xen_set_dynamic_sysbus(), so we only need to add amd-iommu and
intel-iommu.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Marcel Apfelbaum <marcel.a@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20171125151610.20547-7-ehabkost@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/i386/pc_q35.c

@@ -42,6 +42,8 @@
 #include "exec/address-spaces.h"
 #include "hw/i386/pc.h"
 #include "hw/i386/ich9.h"
+#include "hw/i386/amd_iommu.h"
+#include "hw/i386/intel_iommu.h"
 #include "hw/smbios/smbios.h"
 #include "hw/ide/pci.h"
 #include "hw/ide/ahci.h"
@@ -299,8 +301,8 @@ static void pc_q35_machine_options(MachineClass *m)
     m->default_machine_opts = "firmware=bios-256k.bin";
     m->default_display = "std";
     m->no_floppy = 1;
-    /*TODO: allow only sysbus devices that really work with this machine */
-    machine_class_allow_dynamic_sysbus_dev(m, TYPE_SYS_BUS_DEVICE);
+    machine_class_allow_dynamic_sysbus_dev(m, TYPE_AMD_IOMMU_DEVICE);
+    machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
     m->max_cpus = 288;
 }