drm/i915: Use a separate slab for vmas

vma are more frequently allocated than objects and so should equally
benefit from having a dedicated slab.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1008,6 +1008,8 @@ put_bridge:
 free_priv:
 	if (dev_priv->requests)
 		kmem_cache_destroy(dev_priv->requests);
+	if (dev_priv->vmas)
+		kmem_cache_destroy(dev_priv->vmas);
 	if (dev_priv->objects)
 		kmem_cache_destroy(dev_priv->objects);
 	kfree(dev_priv);
@@ -1094,6 +1096,8 @@ int i915_driver_unload(struct drm_device *dev)
 
 	if (dev_priv->requests)
 		kmem_cache_destroy(dev_priv->requests);
+	if (dev_priv->vmas)
+		kmem_cache_destroy(dev_priv->vmas);
 	if (dev_priv->objects)
 		kmem_cache_destroy(dev_priv->objects);