RDMA/nldev: Provide global resource utilization

Expose through the netlink interface the global per-device utilization of
the supported object types.

Provide both dumpit and doit callbacks.

As an example of possible output from rdmatool for system with 5
mlx5 cards:

$ rdma res
1: mlx5_0: qp 4 cq 5 pd 3
2: mlx5_1: qp 4 cq 5 pd 3
3: mlx5_2: qp 4 cq 5 pd 3
4: mlx5_3: qp 2 cq 3 pd 2
5: mlx5_4: qp 4 cq 5 pd 3

Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>