Add IOCTL to translate nvdX into nvmeY and NSID.

While very useful by itself, it also makes nvmecontrol not depend on
hardcoded device names parsing, that in its turn makes simple to take
nvdX (and potentially any other) device names as arguments.

Also added IOCTL bypass from nvdX to respective nvmeYnsZ makes them
interchangeable for management purposes.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.