RDMA/hns: Add roce dfx of arm_cnt

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

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This patch add a way of querying arm_cnt in rdfx.

Reviewed-by: Hu Chunzhi <huchunzhi@huawei.com>
Signed-off-by: Zhao Weibo <zhaoweibo3@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>