logind: explicitly create state directories during early initialization

logind: explicitly create state directories during early initialization

Strictly speaking this isn't necessary for the /run/systemd/seats/
directory, since that is created anyway as the first seat is found, and
seat0 is always found. But let's be explicit here, and also create the
sessions/ and users/ directories, so that people can always install
inotify watches from very early on, even when nobody logged in yet.