[IA64] if idle doesn't halt, it should at least relax

Asit Mallick pointed out that the ia64 idle loop needs a
"hint @pause" instruction in the cases where we don't
actually halt the cpu.
Acked-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/process.c

@@ -187,6 +187,8 @@ default_idle (void)
 	while (!need_resched())
 		if (pal_halt && !pmu_active)
 			safe_halt();
+		else
+			cpu_relax();
 }
 
 #ifdef CONFIG_HOTPLUG_CPU