net/mlx5e: Convert rep stats to mlx5e_stats_grp-based infra

In order to support all of the supported stats that are available in legacy
mode for switchdev uplink representors, convert rep stats infrastructure to
reuse struct mlx5e_stats_grp that is already used when device is in legacy
mode. Refactor rep code to use array of mlx5e_stats_grp
structures (constructed using macros provided by stats infra) to
fill/update stats, instead of fixed hardcoded set of values. This approach
allows to easily extend representors with new stats types.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>