IB/mlx5: Add flow counters binding support

Associates a counters with a flow when IB_FLOW_SPEC_ACTION_COUNT is part
of the flow specifications.

The counters user space placements of location and description (index,
description) pairs are passed as private data of the counters flow
specification.

Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>