vfio/mlx5: Expose migration commands over mlx5 device

Expose migration commands over the device, it includes: suspend, resume,
get vhca id, query/save/load state.

As part of this adds the APIs and data structure that are needed to manage
the migration data.

Link: https://lore.kernel.org/all/20220224142024.147653-13-yishaih@nvidia.com
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>