libata: add another IRQ calls (libata drivers)

This patch is against each libata driver.

Two IRQ calls are added in ata_port_operations.
- irq_on() is used to enable interrupts.
- irq_ack() is used to acknowledge a device interrupt.

In most drivers, ata_irq_on() and ata_irq_ack() are used for
irq_on and irq_ack respectively.

In some drivers (ex: ahci, sata_sil24) which cannot use them
as is, ata_dummy_irq_on() and ata_dummy_irq_ack() are used.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Akira Iguchi <akira2.iguchi@toshiba.co.jp>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/sata_sx4.c b/drivers/ata/sata_sx4.c
index f83038c..06e87a3 100644
--- a/drivers/ata/sata_sx4.c
+++ b/drivers/ata/sata_sx4.c
@@ -207,6 +207,8 @@
 	.eng_timeout		= pdc_eng_timeout,
 	.irq_handler		= pdc20621_interrupt,
 	.irq_clear		= pdc20621_irq_clear,
+	.irq_on			= ata_irq_on,
+	.irq_ack		= ata_irq_ack,
 	.port_start		= pdc_port_start,
 };