net/mlx5: Make MLX5_EN_TLS non-prompt

TLS runs only over Eth, and the Eth driver is the only user of
the core TLS functionality.
There is no meaning of having the core functionality without the usage
in Eth driver.
Hence, let both TLS core implementations depend on MLX5_CORE_EN,
and select MLX5_EN_TLS.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>