scsi: hisi_sas: Add BIST support for fixed code pattern

Through the new debugfs interface the user can select fixed code
patterns. Add two new interfaces fixed_code and fixed_code1.

Link: https://lore.kernel.org/r/1598958790-232272-7-git-send-email-john.garry@huawei.com


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>