hisi_sas: add hisi_sas_slot_abort()

Add a function to abort a slot (task) in the target
device and then cleanup and complete the task.
The function is called from work queue context as
it cannot be called from the context where it is
triggered (interrupt).
Flag hisi_sas_slot.abort is added as the flag used
in the slot error handler to indicate whether the
slot needs to be aborted in the sdev prior to
cleanup and finish.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>