nvme: add uevent variables for controller devices

When we send uevents to userspace, add controller specific
environment variables to uniquly identify the controller beyond
its device name.

This will be useful to address discovery log change events by
actually verifying that the discovery controller is indeed the
same as the device that generated the event.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>