net/mlx5: Add flow counter bulk infrastructure

Add infrastructure to track bulks of flow counters, providing
the means to allocate and deallocate bulks, and to acquire and
release individual counters from the bulks.

Signed-off-by: Gavi Teitz <gavi@mellanox.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>