bhyve: implement NVMe Namespace Identification Descriptor

NVMe 1.3 compliant controllers must implement the Namespace
Identification Descriptor structure (i.e. CNS=3). Previously this was
unimplemented.

Fixes UNH Test 1.1.4-0

Tested by: Jason Tubnor
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D24884