drm/i915: skip LVDS initialization on Apple Mac Mini

The Apple Mac Mini falsely reports LVDS.  Use DMI to check whether we
are running on a Mac Mini, and skip LVDS initialization if that proves
to be the case.

Signed-off-by: Paul Collins <paul@ondioline.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>