net/mlx5: Move iseg access helper routines close to mlx5_core driver

Only mlx5_core driver handles fw initialization check and command
interface revision check.
Hence move them inside the mlx5_core driver where it is used.
This avoid exposing these helpers to all mlx5 drivers.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>