drm/i915: CRC source selection #defines for gmch/vlv chips

A bit a mess, since with DP/TV outputs we can't use the pipe CRC.
Also, no plane CRCs, so we need to update the basic testcases.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>