We forgot to set .has_alpha=true for the A+CCS formats when the code
started to consult .has_alpha. This manifests as A+CCS being treated
as X+CCS which means no per-pixel alpha blending. Fix the format
list appropriately.

Cc: stable@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Heinrich Fink <heinrich.fink@daqri.com>
Reported-by: Heinrich Fink <heinrich.fink@daqri.com>
Tested-by: Heinrich Fink <heinrich.fink@daqri.com>
Fixes: b2081525 ("drm/i915: Add plane alpha blending support, v2.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190603142500.25680-1-ville.syrjala@linux.intel.comReviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>