drm/i915: reorganize intel_lvds_supported

Now it returns false for all platforms unless they're explicitly
listed on the function. There should be no real difference, except for
the fact that it now returns false on Haswell.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>