[POWERPC] ipic: ack only for edge interrupts

Only external interrupts in edge detect mode support ack operation.
Therefore, in most cases ack is not needed.  The patch makes ipic
ack only when it's needed.  This could boost over all system performance.
Signed-off-by: Li Yang <leoli@freescale.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/sysdev/ipic.h

@@ -44,13 +44,11 @@ struct ipic {
 
 	/* The remapper for this IPIC */
 	struct irq_host		*irqhost;
-
-	/* The "linux" controller struct */
-	struct irq_chip		hc_irq;
 };
 
 struct ipic_info {
-	u8	pend;		/* pending register offset from base */
+	u8	ack;		/* pending register offset from base if the irq
+				   supports ack operation */
 	u8	mask;		/* mask register offset from base */
 	u8	prio;		/* priority register offset from base */
 	u8	force;		/* force register offset from base */