bhyve nvme: Add Select support to Get Features

Implement basic support for the SEL field of Get Features. This returns
information about Namespace Specific features.

Fixes UNH ILO 16.0 Test 1.2, Case 13

Reviewed by: imp, allanjude
Tested by: jason@tubnor.net
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D33574