drm: rcar-du: Enable alpha property on primary planes

If the alpha property is not added to a plane, a default value will be
used, which can result in a non-visible layer if the alpha is
initialised as 0.

Provide an alpha blend property on all planes.

Fixes: 161ad653d6c9 ("drm: rcar-du: Use __drm_atomic_helper_plane_reset
instead of copying the logic")

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
1 file changed