net/mlx5: Expose HW capability bits for port buffer per priority congestion counters

Map capability bit indicating that HCA supports port buffer's congestion
counters. Also map registers with the corresponding counters.

Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>