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/include/linux/ide.h b/include/linux/ide.h
index 659b60a..19db0a4 100644
--- a/include/linux/ide.h
+++ b/include/linux/ide.h
@@ -1259,6 +1259,8 @@
 	IDE_HFLAG_ERROR_STOPS_FIFO	= (1 << 19),
 	/* serialize ports */
 	IDE_HFLAG_SERIALIZE		= (1 << 20),
+	/* use legacy IRQs */
+	IDE_HFLAG_LEGACY_IRQS		= (1 << 21),
 };
 
 #ifdef CONFIG_BLK_DEV_OFFBOARD