IB/mlx5: Add function to read WQE from user-space

Add a helper function mlx5_ib_read_user_wqe to read information from
user-space owned work queues.  The function will be used in a later
patch by the page-fault handling code in mlx5_ib.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>

[ Add stub for ib_umem_copy_from() for CONFIG_INFINIBAND_USER_MEM=n
  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/include/linux/mlx5/qp.h b/include/linux/mlx5/qp.h
index 3fa075d..67f4b96 100644
--- a/include/linux/mlx5/qp.h
+++ b/include/linux/mlx5/qp.h
@@ -189,6 +189,9 @@
 	__be32			imm;
 };
 
+#define MLX5_WQE_CTRL_DS_MASK 0x3f
+#define MLX5_WQE_DS_UNITS 16
+
 struct mlx5_wqe_xrc_seg {
 	__be32			xrc_srqn;
 	u8			rsvd[12];