IB/mlx5: Manage device uid for DEVX white list commands

Manage device uid for DEVX white list commands.  The created device uid
will be used on white list commands if the user didn't supply its own uid.

This will enable the firmware to filter out non privileged functionality
as of the recognition of the uid.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>