libata-sff: port_task is SFF specific

port_task is tightly bound to the standard SFF PIO HSM implementation.
Using it for any other purpose would be error-prone and there's no
such user and if some drivers need such feature, it would be much
better off using its own.  Move it inside CONFIG_ATA_SFF and rename it
to sff_pio_task.

The only function which is exposed to the core layer is
ata_sff_flush_pio_task() which is renamed from ata_port_flush_task()
and now also takes care of resetting hsm_task_state to HSM_ST_IDLE,
which is possible as it's now specific to PIO HSM.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_mv.c

@@ -2262,7 +2262,7 @@ static unsigned int mv_qc_issue_fis(struct ata_queued_cmd *qc)
 	}
 
 	if (qc->tf.flags & ATA_TFLAG_POLLING)
-		ata_pio_queue_task(ap, qc, 0);
+		ata_sff_queue_pio_task(ap, 0);
 	return 0;
 }