net/mlx5e: Move params logic into its dedicated file

Take params logic out of en_main.c, into the dedicated params.c.
Some functions are now hidden and become static.
No functional change here.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Aya Levin <ayal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>