vfio: Mark cdev usage in vfio_device

vfio: Mark cdev usage in vfio_device

This can be used to differentiate whether to report group_id or devid in
the revised VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl. At this moment, no
cdev path yet, so the vfio_device_cdev_opened() helper always returns false.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Tested-by: Terrence Xu <terrence.xu@intel.com>
Tested-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718105542.4138-7-yi.l.liu@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>