RDMA/hns: Encapsulate the qp db as a function

Encapsulate qp db into two functions: user and kernel.

Link: https://lore.kernel.org/r/1629985056-57004-7-git-send-email-liangwenpeng@huawei.com


Signed-off-by: Yixing Liu <liuyixing1@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>