improve treatment of NVME devices (bsc#1200975)

[wfeldt]

Task

• https://trello.com/c/JIiwsD3g
• https://bugzilla.suse.com/show_bug.cgi?id=1200975

NVME devices that are not directly attached to PCI are not shown properly.

Solution

Treat NVME devices as their own device class.