net/mlx5: Introduce attach/detach to interface API

Add attach/detach callbacks to interface API.
This is crucial for implementing seamless reset flow which releases the
hardware and it's resources upon detach while keeping software
structures and state (e.g netdev) then reset and reallocate the hardware
needed resources upon attach.

Signed-off-by: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>