drm/atomic: Initialise planes with opaque alpha values

Planes without an alpha property, using __drm_atomic_helper_plane_reset
will have their plane state alpha initialised as zero, which represents
a transparent alpha.

If this value is then used for the plane, it may not be visible by
default, and thus doesn't represent a good initialisation state.

Update the default state->alpha value to DRM_BLEND_ALPHA_OPAQUE
unconditionally when the plane is reset.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180919155700.10342-2-kieran.bingham+renesas@ideasonboard.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -3569,9 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
 	state->plane = plane;
 	state->rotation = DRM_MODE_ROTATE_0;
 
-	/* Reset the alpha value to fully opaque if it matters */
-	if (plane->alpha_property)
-		state->alpha = plane->alpha_property->values[1];
+	state->alpha = DRM_BLEND_ALPHA_OPAQUE;
 	state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
 
 	plane->state = state;