scsi: hisi_sas: Debugfs global register create file and add file operations

scsi: hisi_sas: Debugfs global register create file and add file operations

BugLink: https://bugs.launchpad.net/bugs/1819500
This patch create debugfs file for global register and add file
operations.

Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from commit caefac1996764d19e4fa39d8d33651da257dcab2)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>