tmpfiles: create static device nodes before udev is started
Since v183, the contents of /usr/lib/udev/devices is no longer copied to /dev on boot, rather systemd-tmpfiles should be used instead. However, as systemd-tmpfiles --create is only ran long after udevd has been started, it is no longer possible to use udev rules to assign permissions to the static nodes. This calls systemd-tmpfiles --create early, before udev is started, and restricts the call to /dev, which is known to be mounted already. In the future, this could also take over the creation of static device nodes from systemd-udevd.