net/mlx5: Add helper function to release fw page

Factor out the fwp address release page to an helper function, will be
used in the downstream patch.

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>