ctl: Add helper routines to populate NVMe namespace data IDs for a LUN

These will be used by the backends to populate the unique ID fields
like EUI64 in the NVMe namespace data (CNS == 0) and namespace
identification descriptor list (CNS == 3).

Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44721