Revert "virtio: improve virtio devices initialization time"

This reverts commit 6f0bb230.

This reverts commit f87d72f5 as that is
reported to break cleanup and migration.

Cc: Gal Hammer <ghammer@redhat.com>
Cc: Sitong Liu <siliu@redhat.com>
Cc: Xiaoling Gao <xiagao@redhat.com>
Suggested-by: NGreg Kurz <groug@kaod.org>
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Reported-by: NJose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
Reported-by: NDaniel Henrique Barboza <danielhb@linux.vnet.ibm.com>

hw/virtio/virtio.c

@@ -2574,7 +2574,6 @@ static int virtio_device_start_ioeventfd_impl(VirtIODevice *vdev)
     VirtioBusState *qbus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev)));
     int n, r, err;
 
-    memory_region_transaction_begin();
     for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
         VirtQueue *vq = &vdev->vq[n];
         if (!virtio_queue_get_num(vdev, n)) {
@@ -2597,7 +2596,6 @@ static int virtio_device_start_ioeventfd_impl(VirtIODevice *vdev)
         }
         event_notifier_set(&vq->host_notifier);
     }
-    memory_region_transaction_commit();
     return 0;
 
 assign_error:
@@ -2611,7 +2609,6 @@ assign_error:
         r = virtio_bus_set_host_notifier(qbus, n, false);
         assert(r >= 0);
     }
-    memory_region_transaction_commit();
     return err;
 }
 
@@ -2628,7 +2625,6 @@ static void virtio_device_stop_ioeventfd_impl(VirtIODevice *vdev)
     VirtioBusState *qbus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev)));
     int n, r;
 
-    memory_region_transaction_begin();
     for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
         VirtQueue *vq = &vdev->vq[n];
 
@@ -2639,7 +2635,6 @@ static void virtio_device_stop_ioeventfd_impl(VirtIODevice *vdev)
         r = virtio_bus_set_host_notifier(qbus, n, false);
         assert(r >= 0);
     }
-    memory_region_transaction_commit();
 }
 
 void virtio_device_stop_ioeventfd(VirtIODevice *vdev)