drm/i915:: Disable FBC on SandyBridge

Enabling FBC is causing the BLT ring to run between 10-100x slower than
normal and frequently lockup. The interim solution is disable FBC once
more until we know why.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -1872,7 +1872,7 @@ static void intel_update_fbc(struct drm_device *dev)
 	if (enable_fbc < 0) {
 		DRM_DEBUG_KMS("fbc set to per-chip default\n");
 		enable_fbc = 1;
-		if (INTEL_INFO(dev)->gen <= 5)
+		if (INTEL_INFO(dev)->gen <= 6)
 			enable_fbc = 0;
 	}
 	if (!enable_fbc) {