nvmft: Add NVMeoF controller routines shared between kernel and userland

This includes functions to validate NVMe Qualified Names, compute an
initial value of the CAP property, validate changes to the CC
property, and populate the Identify Controller data structure for an
I/O controller.

Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44709