net/mlx5: DR, Add infrastructure for supporting several steering formats

Add a struct of device specific callbacks for STE layer below dr_ste.
Each device will implement its HW-specific function, and a comon logic
from the DR code will access these functions through the new ste_ctx API.

More callbacks will follow in the subsequent patches.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>