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