ivi-shell: fix cleanup of desktop surfaces

The ivi-shell keeps track of its surfaces by adding them to the ivi_surface_list to be able to remove them on shutdown. It also creates an ivi_layout_surface for a desktop surface, but does not keep track of these surfaces.

During compositor shutdown, the IVI-shell therefore prints the following error:

BUG: finalizing a layer with views still on it.

Fix it by adding the created ivi_layout_surface to the ivi_surface_list to remove the surfaces from the layer during shutdown.

Furthermore, remove the ivi_layout_surface from the desktop surface and free it when the desktop surface is destroyed.