drm/i915/bdw: Disable semaphores for Execlists

Up until recently, semaphores weren't enabled in BDW so we didn't care
about them. But then Rodrigo came and enabled them:

   commit 521e62e49a
   Author: Rodrigo Vivi <rodrigo.vivi@intel.com>

      drm/i915: Enable semaphores on BDW

So now we have to explicitly disable them for Execlists until both
features play nicely.

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -481,6 +481,10 @@ bool i915_semaphore_is_enabled(struct drm_device *dev)
 	if (i915.semaphores >= 0)
 		return i915.semaphores;
 
+	/* TODO: make semaphores and Execlists play nicely together */
+	if (i915.enable_execlists)
+		return false;
+
 	/* Until we get further testing... */
 	if (IS_GEN8(dev))
 		return false;