vfio: Make vfio_device_open() truly device specific

Then move group related logic into vfio_device_open_file(). Accordingly
introduce a vfio_device_close() to pair up.

Link: https://lore.kernel.org/r/20221201145535.589687-7-yi.l.liu@intel.com


Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Tested-by: Yu He <yu.he@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>