Simplify -devel subpackage packaging
    
    Instead of 4 subpackages, wayland-devel + libwayland-client-devel +
    libwayland-cursor-devel + libwayland-server-devel, just have a single
    wayland-devel that has all the headers needed for linking.
    
    This way, we can have a single -devel package which makes it easier to
    install wayland headers to develop with it, but at the same time keeps
    library subpackages separate so that the binary distro doesn't pull in
    unneeded dependencies.