drm/i915:Initialize the second BSD ring on BDW GT3 machine

Based on the hardware spec, the BDW GT3 machine has two independent
BSD ring that can be used to dispatch the video commands.
So just initialize it.

V3->V4: Follow Imre's comment to do some minor updates. For example:
more comments are added to describe the semaphore between ring.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
[danvet: Fix up checkpatch error.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7d6acb4..5411079 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1834,7 +1834,9 @@
 #define BSD_RING		(1<<VCS)
 #define BLT_RING		(1<<BCS)
 #define VEBOX_RING		(1<<VECS)
+#define BSD2_RING		(1<<VCS2)
 #define HAS_BSD(dev)            (INTEL_INFO(dev)->ring_mask & BSD_RING)
+#define HAS_BSD2(dev)		(INTEL_INFO(dev)->ring_mask & BSD2_RING)
 #define HAS_BLT(dev)            (INTEL_INFO(dev)->ring_mask & BLT_RING)
 #define HAS_VEBOX(dev)            (INTEL_INFO(dev)->ring_mask & VEBOX_RING)
 #define HAS_LLC(dev)            (INTEL_INFO(dev)->has_llc)