compositor: use weston_view_is_opaque() to check for opacity in debug_scene_view_print()

Currently the debug output for 'drm-backend' can be confusing. In the output of debug_scene_view_print() views may be listed as 'not opaque' but later, during plane assignment, other views underneath such a view is reported as 'occluded on our output'. This happens because weston_view_is_opaque() has some extra checks to determine if a view is fully opaque, such as 'is_opaque' provided by the renderer for formats that have no alpha channel.

Use weston_view_is_opaque() in debug_scene_view_print() as well to get more accurate results.

Signed-off-by: Michael Olbrich m.olbrich@pengutronix.de