RDMA/mlx5: Introduce ODP prefetch counter

For debugging purpose it will be easier to understand if prefetch works
okay if it has its own counter. Introduce ODP prefetch counter and count
per MR the total number of prefetched pages.

In addition remove comment which is not relevant anymore and anyway not in
the correct place.

Link: https://lore.kernel.org/r/20200621104147.53795-1-leon@kernel.org
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/ib_verbs.h

@@ -2271,6 +2271,7 @@ struct rdma_netdev_alloc_params {
 struct ib_odp_counters {
 	atomic64_t faults;
 	atomic64_t invalidations;
+	atomic64_t prefetch;
 };
 
 struct ib_counters {