Add 'vfio' mode to pkg/nvcdi for generating CDI specs for NVIDIA pass…

[elezar]

…through GPUs

./nvidia-ctk cdi generate --mode=vfio
WARN[0000] Failed to locate nvidia-ctk: pattern nvidia-ctk not found
INFO[0000] Generated CDI spec with version 0.5.0
---
cdiVersion: 0.5.0
containerEdits: {}
devices:
- containerEdits:
    deviceNodes:
    - path: /dev/vfio/46
  name: "0"
- containerEdits:
    deviceNodes:
    - path: /dev/vfio/46
  name: all
kind: nvidia.com/gpu

[elezar]

@cdesiniotis if this is still valid, please rebase or close.