drm/i915: Conditionally carve out GGTT PDE

It only works that way on GEN6 and GEN7. Let's not assume GENn will be
the same.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
1 file changed