drm/i915: Disable RCS flips on Ivybridge

We currently see random GPU hangs when using RCS flips with multiple
pipes on Ivybridge. Now that we have mmio flips, we can fairly cheaply
fallback to using CPU driven flips instead.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77104Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -9658,6 +9658,8 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 
 	if (IS_VALLEYVIEW(dev)) {
 		ring = &dev_priv->ring[BCS];
+	} else if (IS_IVYBRIDGE(dev)) {
+		ring = &dev_priv->ring[BCS];
 	} else if (INTEL_INFO(dev)->gen >= 7) {
 		ring = obj->ring;
 		if (ring == NULL || ring->id != RCS)