drm/i915/bdw: Disable semaphores

We've done insufficient testing on them thus far, so keep them disabled
until we do test.

v2: Use WARN when not enabling preliminary HW support as this should
only be disabled for that case.

v3: Rip out the now useless (and really noisy) DRM_INFO output.

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuosugeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -478,6 +478,12 @@ bool i915_semaphore_is_enabled(struct drm_device *dev)
 	if (INTEL_INFO(dev)->gen < 6)
 		return 0;
 
+	/* Until we get further testing... */
+	if (IS_GEN8(dev)) {
+		WARN_ON(!i915_preliminary_hw_support);
+		return 0;
+	}
+
 	if (i915_semaphores >= 0)
 		return i915_semaphores;