RDMA/mlx5: Use stages for callback to setup and release DEVX

Reuse existing infrastructure to initialize and release DEVX uid.
The DevX interface is intended for user space access, so it is supposed
to be initialized before ib_register_device(). Also it isn't supported
in switchdev mode and don't need to initialize it in that mode.

Fixes: 76dc5a84

 ("IB/mlx5: Manage device uid for DEVX white list commands")
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>