drm/i915: Remove ARBG/ABGR 2101010 on platform not supporting those formats

We just have have VLV and CHV sprites programming the hardware
differently for the ABGR2101010 so keep them working.

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