scsi: hisi_sas: Add trace FIFO debugfs support

The controller provides trace FIFO DFX tool to assist link fault debugging
and link optimization. This tool can be helpful when debugging link faults
without SAS analyzers. Each PHY has an independent trace FIFO interface.

The user can configure the trace FIFO tool of one PHY by using the
following six interfaces:

signal_sel: select signal group applies to different scenarios.
  0x0: linkrate negotiation
  0x1: Host 12G TX train
  0x2: Disk 12G TX train
  0x3: SAS PHY CTRL DFX 0
  0x4: SAS PHY CTRL DFX 1
  0x5: SAS PCS DFX
  other: linkrate negotiation
dump_mask: The masked hardware status bit will not be updated.
dump_mode: determines how to dump data after trigger signal is generated.
  0x0: dump forever
  0x1: dump 32 data after trigger signal is generated
  0x2: no more dump after trigger signal is generated
trigger_mode: determines the trigger mode, level or edge.
  0x0: dump when trigger signal changed
  0x1: dump when trigger signal's level equal to trigger_level
  0x2: dump when trigger signal's level different from trigger_level
trigger_level: determines the trigger level.
trigger_msk: mask trigger signal

The user can get 32-byte values from hardware by reading the rd_data.
These values consitute the status record of the hardware at different time
points.

Link: https://lore.kernel.org/r/1611659068-131975-6-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>

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