compositor: Let renderers create and destroy surface state on their own

Remove create_surface() and destroy_surface() from the renderer
interface and change the renderers to create surface state on demand
and destroy it using the weston_surface's destroy signal.

Also make sure the surfaces' renderer state is reset to NULL on
destruction.

This is a step towards runtime switchable renderers.

(rpi-renderer changes are only compile-tested)
6 files changed