drm/i915: Use a separate slab for requests

requests are even more frequently allocated than objects and equally
benefit from having a dedicated slab.

v2: Rebase

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 8f5428b..180b5d9 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1006,8 +1006,10 @@
 put_bridge:
 	pci_dev_put(dev_priv->bridge_dev);
 free_priv:
-	if (dev_priv->slab)
-		kmem_cache_destroy(dev_priv->slab);
+	if (dev_priv->requests)
+		kmem_cache_destroy(dev_priv->requests);
+	if (dev_priv->objects)
+		kmem_cache_destroy(dev_priv->objects);
 	kfree(dev_priv);
 	return ret;
 }
@@ -1090,8 +1092,10 @@
 	if (dev_priv->regs != NULL)
 		pci_iounmap(dev->pdev, dev_priv->regs);
 
-	if (dev_priv->slab)
-		kmem_cache_destroy(dev_priv->slab);
+	if (dev_priv->requests)
+		kmem_cache_destroy(dev_priv->requests);
+	if (dev_priv->objects)
+		kmem_cache_destroy(dev_priv->objects);
 
 	pci_dev_put(dev_priv->bridge_dev);
 	kfree(dev_priv);