ide: add IDE_HFLAG_LEGACY_IRQS host flag

Add IDE_HFLAG_LEGACY_IRQS host flag to tell ide_pci_setup_ports() to set
hwif->irq to legacy IRQ 14/15 (iff hwif->irq is not already set) and convert
atiixp, piix, serverworks, sis5513 and slc90e66 host drivers to use it.

While at it:

* In piix.c add IDE_HFLAGS_PIIX define and don't use ->init_hwif for MPIIX.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/setup-pci.c b/drivers/ide/setup-pci.c
index aae4806f..7989f52 100644
--- a/drivers/ide/setup-pci.c
+++ b/drivers/ide/setup-pci.c
@@ -562,6 +562,9 @@
 		if ((d->host_flags & IDE_HFLAG_NO_DMA) == 0)
 			ide_hwif_setup_dma(dev, d, hwif);
 
+		if ((d->host_flags & IDE_HFLAG_LEGACY_IRQS) && hwif->irq == 0)
+			hwif->irq = port ? 15 : 14;
+
 		hwif->host_flags = d->host_flags;
 		hwif->pio_mask = d->pio_mask;