RDMA/hns: Refactor mtr_init_buf_cfg()

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Y79T



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page_shift and page_cnt is only used in mtr_map_bufs(). And these
parameter could be calculated indepedently.

Strip the computation of page_shift and page_cnt from mtr_init_buf_cfg(),
reducing the number of parameters of it. This help reducing coupling
between mtr_inif_buf_cfg() and mtr_map_bufs().

And the parameter validation in mtr_init_buf_cfg has also been abstracted
into a separate function and placed at the beginning of the function.

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Reviewed-by: Yangyang Li <liyangyang20@huawei.com>
Reviewed-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>