bhyve: Create EUI64 for NVMe namespaces

Accept an IEEE Extended Unique Identifier (EUI-64) from the command
line for each NVMe namespace. If one isn't provided, it will create one
based on the CRC16 of:

• the FreeBSD IEEE OUI
• PCI bus, device/slot, function values
• Namespace ID

Reviewed by: imp, araujo, jhb, rgrimes
Approved by: imp (mentor), jhb (maintainer)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D19905