RDMA/hns: Optimize MTR level-0 addressing to access huge page

If hns ROCEE is set to level-0 addressing, the length of the entire buffer
can be used as the page size. The driver needn't to split the buffer into
small units because all pages are continuous.

Link: https://lore.kernel.org/r/1593525696-12570-1-git-send-email-liweihang@huawei.com


Signed-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>