drm/i915: No LLC_MLC for HSW.

The mid-level cache or as it's more commonly referred to now as L3, is
not setup this way on HSW.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>