net/mlx5: Expose DC scatter to CQE capability bit

dc_req_scat_data_cqe capability bit determines
if requester scatter to cqe is available for 64 bytes CQE over
DC transport type.

Signed-off-by: Yonatan Cohen <yonatanc@mellanox.com>
Reviewed-by: Guy Levi <guyle@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>