RDMA/hns: Support flush cqe for hip08 in kernel space

According to IB protocol, there are some cases that work requests must
return the flush error completion status through the completion queue. Due
to hardware limitation, the driver needs to assist the flush process.

This patch adds the support of flush cqe for hip08 in the cases that
needed, such as poll cqe, post send, post recv and aeqe handle.

The patch also considered the compatibility between kernel and user space.

Signed-off-by: Yixian Liu <liuyixian@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>