drm/i915: Enable DP port CRC for the "auto" source on g4x/vlv

Now that DP port CRCs are stable, we can use it for generic CRC tests.
Yay, the auto CRC source should now work everywhere!

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>