Following the refactoring of device request extraction, we can
now make CDI device requests consistent with other methods.
This change moves to using image.VisibleDevices instead of
separate calls to CDIDevicesFromMounts and VisibleDevicesFromEnvVar.
The handling of annotation-based requests will be addressed in a
follow-up.
Signed-off-by: Evan Lezar <elezar@nvidia.com>