net/mlx5e: Make flow steering arfs independent of priv

Decouple arfs flow steering functionality from priv.
Make all arfs functions defined under fs.h get flow_steering
struct as an argument, thus helping with the process of decoupling the
whole flow steering API from en.h.

Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>