drm/i915: Disable MI_SET_CONTEXT psmi w/a for bdw

The current w/a for the gen7 psmi related hangs doesn't apply to bdw, so
disable it if using bdw ringbuffer submission.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170324151724.32640-1-chris@chris-wilson.co.ukReviewed-by: NMichał Winiarski <michal.winiarski@intel.com>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -582,8 +582,8 @@ mi_set_context(struct drm_i915_gem_request *req, u32 flags)
 	struct intel_engine_cs *engine = req->engine;
 	enum intel_engine_id id;
 	const int num_rings =
-		/* Use an extended w/a on ivb+ if signalling from other rings */
-		i915.semaphores ?
+		/* Use an extended w/a on gen7 if signalling from other rings */
+		(i915.semaphores && INTEL_GEN(dev_priv) == 7) ?
 		INTEL_INFO(dev_priv)->num_rings - 1 :
 		0;
 	int len;