qemu_vm: introduce amd-iommu

Introduce `amd-iommu` device to guests. Configuration example:

    ```
    vm_iommu_model = amd
    iommu_$foo = ...
    iommu_$bar = ...
    ```

Signed-off-by: Xu Han <xuhan@redhat.com>

virttest/qemu_vm.py

@@ -1914,6 +1914,18 @@ def __iothread_conflict_check(params):
             )
             devices.insert(dev)
 
+        if params.get("vm_iommu_model") == "amd" and devices.has_device("amd-iommu"):
+            iommu_params = {
+                "device-iotlb": params.get("iommu_device_iotlb"),
+                "intremap": params.get("iommu_intremap"),
+                "pt": params.get("iommu_pt"),
+                "xtsup": params.get("iommu_xtsup"),
+            }
+            parent_bus = {"type": "PCIE"}
+            dev = QDevice("amd-iommu", iommu_params, parent_bus=parent_bus)
+            set_cmdline_format_by_cfg(dev, self._get_cmdline_format_cfg(), "iommu_dev")
+            devices.insert(dev)
+
         # Add device virtio-iommu, it must be added before any virtio devices
         if params.get_boolean("virtio_iommu") and devices.has_device(
             "virtio-iommu-pci"