RDMA/hns: Refactor mailbox functions

The current mailbox functions have too many parameters, making the code
difficult to maintain. So construct a new structure mbox_msg to pass the
information needed by mailbox.

Link: https://lore.kernel.org/r/20220302064830.61706-6-liangwenpeng@huawei.com


Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>