i915: use alloc_ordered_workqueue() instead of explicit UNBOUND w/ max_active = 1

This is an equivalent conversion and will ease scheduled removal of
WQ_NON_REENTRANT.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1558,11 +1558,9 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	 *
 	 * All tasks on the workqueue are expected to acquire the dev mutex
 	 * so there is no point in running more than one instance of the
-	 * workqueue at any time: max_active = 1 and NON_REENTRANT.
+	 * workqueue at any time.  Use an ordered one.
 	 */
-	dev_priv->wq = alloc_workqueue("i915",
-				       WQ_UNBOUND | WQ_NON_REENTRANT,
-				       1);
+	dev_priv->wq = alloc_ordered_workqueue("i915", 0);
 	if (dev_priv->wq == NULL) {
 		DRM_ERROR("Failed to create our workqueue.\n");
 		ret = -ENOMEM;