Revert "qemu: forbid migration with an IOMMU device"

This reverts commit b7118623.

Migration was implemented by QEMU commit:
commit 8cdcf3c1e58d04b6811956d7608efeb66c42d719
Author: Peter Xu <peterx@redhat.com>
Date:   Fri Jan 6 12:06:13 2017 +0800

    intel_iommu: allow migration

https://bugzilla.redhat.com/show_bug.cgi?id=1433994

src/qemu/qemu_migration.c

@@ -2359,12 +2359,6 @@ qemuMigrationIsAllowed(virQEMUDriverPtr driver,
                            _("migration with shmem device is not supported"));
             return false;
         }
-
-        if (vm->def->iommu) {
-            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
-                           _("migration with iommu device is not supported"));
-            return false;
-        }
     }
 
     return true;