[libata] improve device scan

Replace SCSI's legacy "bang at the door" method of probing with one
directly controlled by the underlying ATA transport layer.

We now only call scsi_scan_target() for devices we find, rather than
probing every possible channel/id within a certain range.

drivers/scsi/libata-scsi.c

@@ -1678,3 +1678,15 @@ void ata_scsi_simulate(u16 *id,
 	}
 }
 
+void ata_scsi_scan_host(struct ata_port *ap)
+{
+	unsigned int i;
+
+	if (ap->flags & ATA_FLAG_PORT_DISABLED)
+		return;
+
+	for (i = 0; i < ATA_MAX_DEVICES; i++)
+		if (ata_dev_present(&ap->device[i]))
+			scsi_scan_target(&ap->host->shost_gendev, 0, i, ~0, 0);
+}
+