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_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index f9e3295..d521de3 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -80,6 +80,8 @@
 	B(has_overlay);
 	B(overlay_needs_physical);
 	B(supports_tv);
+	B(has_bsd_ring);
+	B(has_blt_ring);
 #undef B
 
 	return 0;