drm/i915/bdw: Disable PPGTT for now

This will be changed once the gen8 code is fully implemented.

v2: Use ENOSYS instead of ENXIO as suggested by Chris.
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -410,6 +410,8 @@ static int i915_gem_init_aliasing_ppgtt(struct drm_device *dev)
 
 	if (INTEL_INFO(dev)->gen < 8)
 		ret = gen6_ppgtt_init(ppgtt);
+	else if (IS_GEN8(dev))
+		ret = -ENOSYS;
 	else
 		BUG();