RDMA/hns: Support SW stats with debugfs

Support SW stats with debugfs.

Query output:
$ cat /sys/kernel/debug/hns_roce/hns_0/sw_stat/sw_stat
aeqe --- 3341
ceqe --- 0
cmds --- 6764
cmds_err --- 0
posted_mbx --- 3344
polled_mbx --- 3
mbx_event --- 3341
qp_create_err --- 0
qp_modify_err --- 0
cq_create_err --- 0
cq_modify_err --- 0
srq_create_err --- 0
srq_modify_err --- 0
xrcd_alloc_err --- 0
mr_reg_err --- 0
mr_rereg_err --- 0
ah_create_err --- 0
mmap_err --- 0
uctx_alloc_err --- 0

Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Link: https://lore.kernel.org/r/20231114123449.1106162-4-huangjunxian6@hisilicon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

RDMA/hns: Add debugfs to hns RoCE

Add debugfs to hns RoCE. This patch only adds an empty directory
"hns_roce" to debugs root directory.

Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://lore.kernel.org/r/20231114123449.1106162-3-huangjunxian6@hisilicon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>