This should really have been added in BDW integration, as well as:

commit 93bd8649
Author: Ben Widawsky <ben@bwidawsk.net>
Date:   Tue Jul 16 16:50:06 2013 -0700

    drm/i915: Put the mm in the parent address space

It didn't really matter before, but it will in the future.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>