libahci: Add support to handle HOST_IRQ_STAT as edge trigger latch.

This patch adds the support to handle HOST_IRQ_STAT as edge trigger
latch.

Signed-off-by: Suman Tripathi <stripathi@apm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
index 71262e0..f442960 100644
--- a/drivers/ata/ahci.h
+++ b/drivers/ata/ahci.h
@@ -238,6 +238,8 @@
 	AHCI_HFLAG_MULTI_MSI		= (1 << 16), /* multiple PCI MSIs */
 	AHCI_HFLAG_NO_DEVSLP		= (1 << 17), /* no device sleep */
 	AHCI_HFLAG_NO_FBS		= (1 << 18), /* no FBS */
+	AHCI_HFLAG_EDGE_IRQ		= (1 << 19), /* HOST_IRQ_STAT behaves as
+							Edge Triggered */
 
 	/* ap->flags bits */