RDMA/hns: Optimize the usage of MTR

Currently, the MTR region is configed before hns_roce_mtr_map() is
invoked, but in some scenarios, the region is configed at MTR creation,
the caller need to store this config and call hns_roce_mtr_map() later. So
optimize the usage by wrapping the MTR region config into MTR.

Link: https://lore.kernel.org/r/1589982799-28728-10-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@mellanox.com>