[libata] ata_piix: Enable parallel scan

This patch turns on parallel scanning for the ata_piix driver.
This driver is used on most netbooks (no AHCI for cheap storage it seems).
The scan is the dominating time factor in the kernel boot for these
devices; with this flag it gets cut in half for the device I used
for testing (eeepc).
Alan took a look at the driver source and concluded that it ought to be safe
to do for this driver.  Alan has also checked with the hardware team.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ata_piix.c

@@ -1589,6 +1589,7 @@ static int __devinit piix_init_one(struct pci_dev *pdev,
 		host->ports[1]->mwdma_mask = 0;
 		host->ports[1]->udma_mask = 0;
 	}
+	host->flags |= ATA_HOST_PARALLEL_SCAN;
 
 	pci_set_master(pdev);
 	return ata_pci_sff_activate_host(host, ata_sff_interrupt, &piix_sht);