util: Introduce virNVMeDevice module

util: Introduce virNVMeDevice module

This module will be used by virHostdevManager and it's inspired
by virPCIDevice module. They are very similar except instead of
what makes a NVMe device: PCI address AND namespace ID. This
means that a NVMe device can appear in a domain multiple times,
each time with a different namespace.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Cole Robinson <crobinso@redhat.com>