[IA64] fix NULL pointer in ia64/irq_chip-mask/unmask function

This patch fixes boot failure because irq_desc->mask() is NULL.

- Added mask/unmask functions to ia64's irq desc function table.
- rename hw_interrupt_type to irq_chip. hw_interrupt_type is old name.
- Tony: Added same change to arch/ia64/sn/kernel/irq.c as pointed out
  by Eric Biederman ... mask/unmask functions there can be no-op.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/arch/ia64/sn/kernel/irq.c b/arch/ia64/sn/kernel/irq.c
index 8c5bee0..8d2a1bf 100644
--- a/arch/ia64/sn/kernel/irq.c
+++ b/arch/ia64/sn/kernel/irq.c
@@ -205,7 +205,17 @@
 		(void)sn_retarget_vector(sn_irq_info, nasid, slice);
 }
 
-struct hw_interrupt_type irq_type_sn = {
+static void
+sn_mask_irq(unsigned int irq)
+{
+}
+
+static void
+sn_unmask_irq(unsigned int irq)
+{
+}
+
+struct irq_chip irq_type_sn = {
 	.name		= "SN hub",
 	.startup	= sn_startup_irq,
 	.shutdown	= sn_shutdown_irq,
@@ -213,6 +223,8 @@
 	.disable	= sn_disable_irq,
 	.ack		= sn_ack_irq,
 	.end		= sn_end_irq,
+	.mask		= sn_mask_irq,
+	.unmask		= sn_unmask_irq,
 	.set_affinity	= sn_set_affinity_irq
 };