net/mlx5: Bridge, move additional data structures to priv header

Following patches in series will require accessing flow tables and groups
sizes, table levels and struct mlx5_esw_bridge from new the new source file
dedicated to multicast code. Expose these data in bridge_priv.h to reduce
clutter in following patches that will implement the actual functionality.

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