net/mlx5e: Add generic macros to use metadata register mapping

There are many definitions to get bits and mask for different types of
metadata register mapping, add generic macros to unify them.

Signed-off-by: Jianbo Liu <jianbol@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Ariel Levkovich <lariel@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>