Claude review: drm/virtio: Freeze and restore hooks to support suspend and resume

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This patch adds `virtgpu_freeze()` / `virtgpu_restore()` and extracts `virtio_gpu_find_vqs()` as a reusable helper. The refactoring of `virtio_gpu_init()` to call the new helper is clean.

**Issue 1 (medium): `wait_event_timeout` return values ignored in freeze**

```c
wait_event_timeout(vgdev->ctrlq.ack_queue,
    vgdev->ctrlq.vq->num_free == vgdev->ctrlq.vq->num_max,
    5 * HZ);

wait_event_timeout(vgdev->cursorq.ack_queue,
    vgdev->cursorq.vq->num_free == vgdev->cursorq.vq->num_max,
    5 * HZ);
```

If either wait times out, the function proceeds to `del_vqs()` without warning. This means in-flight commands could be silently lost. At minimum a `DRM_WARN` on timeout would help debugging; better would be to return an error from freeze, which would abort the hibernation attempt.

**Observation: `del_vqs()` called via `config->del_vqs` vs direct**

In `virtgpu_freeze()`:
```c
vdev->config->del_vqs(vdev);
```

This is fine and matches the style used in `virtio_gpu_deinit()`.

Otherwise the patch is straightforward and correct. The helper extraction is clean.

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