device: skip deserialization of device units when udevd is not running

device: skip deserialization of device units when udevd is not running

Do not try to party initialize a device during deserialization if it's not
known by udev (anymore) and therefore hasn't been seen during device
enumeration.

The device unit in this case has not been initialized properly and setting it
in the "plugged" state can be confusing.

Actually this happens during every boots when PID switches to the new rootfs:
PID is reexecuted and enumerates devices but since udev is not running, the
list of enumerated devices is empty.