drm/i915: Enable SandyBridge blitter ring

Based on an original patch by Zhenyu Wang, this initializes the BLT ring for
SandyBridge and enables support for user execbuffers.

Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 1ffeb1c..1851ca4 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -133,6 +133,7 @@
 	mutex_lock(&dev->struct_mutex);
 	intel_cleanup_ring_buffer(dev, &dev_priv->render_ring);
 	intel_cleanup_ring_buffer(dev, &dev_priv->bsd_ring);
+	intel_cleanup_ring_buffer(dev, &dev_priv->blt_ring);
 	mutex_unlock(&dev->struct_mutex);
 
 	/* Clear the HWS virtual address at teardown */
@@ -763,6 +764,9 @@
 	case I915_PARAM_HAS_BSD:
 		value = HAS_BSD(dev);
 		break;
+	case I915_PARAM_HAS_BLT:
+		value = HAS_BLT(dev);
+		break;
 	default:
 		DRM_DEBUG_DRIVER("Unknown parameter %d\n",
 				 param->param);