mount: set up local-fs.target/remote-fs.target deps in mount_add_default_dependencies...

mount: set up local-fs.target/remote-fs.target deps in mount_add_default_dependencies() too

This deps are very similar to the -pre deps, hence establish them at the
same place, in particular as they should only be generated if default
deps are on.

This allows us to later on remove similar code that adds in these deps
whenever /proc/self/mountinfo changes.