net/mlx5: Bridge, refactor groups sizes and indices

Following patches in the series introduce additional flow groups for QinQ
support. With increased number of groups it becomes cumbersome to calculate
groups sizes as fractions of the table size. Instead, manually define sizes
of specific group types and ensure that totals are still correct by static
assertions. Having specific table size is important for firmware resource
management.

This commit doesn't change functionality.

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