RDMA/mlx5: Support SQD2RTS for modify QP

The transition of the QP state from SQD to RTS is allowed by the IB
specification. The hardware also supports that, but it is not
implemented in mlx5_ib.

This commit adds SQD2RTS command to the modify QP in mlx5_ib to support
the missing feature. The feature is required by the signature pipelining
API that will be added to rdma-core.

Link: https://lore.kernel.org/r/ab4876360bfba0e9d64a5e8599438e32e0cb351e.1620641808.git.leonro@nvidia.com


Reviewed-by: Evgenii Kochetov <evgeniik@nvidia.com>
Signed-off-by: Sergey Gorenko <sergeygo@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>