RDMA/hns: Refactor hem table mhop check and calculation

The calculation of mhop for hem is duplicated in hns_roce_init_hem_table
and hns_roce_calc_hem_mhop, extracting it from them to a separate
function. Moreover, this patch refactors hns_roce_check_whether_mhop to
reduce complexity.

Link: https://lore.kernel.org/r/1562593285-8037-9-git-send-email-oulijun@huawei.com


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