nodedev: udev: Convert udev private data to a lockable object

nodedev: udev: Convert udev private data to a lockable object

Since there's going to be a worker thread which needs to have some data
protected by a lock, the whole code would just simply get unnecessary
complex, since two sets of locks would be necessary, driver lock (for
udev monitor and event handle) and a mutex protecting thread-local data.
Given the future thread will need to access the udev monitor socket as
well, why not protect everything with a single lock, even better, by
converting the driver's private data to a lockable object, we get the
automatic object disposal feature for free.

Signed-off-by: Erik Skultety <eskultet@redhat.com>