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_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index c3decb2..90f9c3e 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -158,12 +158,14 @@
 	.gen = 6,
 	.need_gfx_hws = 1, .has_hotplug = 1,
 	.has_bsd_ring = 1,
+	.has_blt_ring = 1,
 };
 
 static const struct intel_device_info intel_sandybridge_m_info = {
 	.gen = 6, .is_mobile = 1,
 	.need_gfx_hws = 1, .has_hotplug = 1,
 	.has_bsd_ring = 1,
+	.has_blt_ring = 1,
 };
 
 static const struct pci_device_id pciidlist[] = {		/* aka */