net/mlx5: Simplify HW context interfaces by using SA entry

SA context logic used multiple structures to store same data
over and over. By simplifying the SA context interfaces, we
can remove extra structs.

Reviewed-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>