ia64: Make sure interrupts enabled when we "safe_halt()"

In commit d1669912
   idle: Implement generic idle function
Thomas Gleixner cleaned up many things but perturbed some
fragile code that was keeping ia64 alive. So we started
seeing:
   WARNING: at kernel/cpu/idle.c:94 cpu_idle_loop+0x360/0x380()
and other unpleasantness like system hangs during boot.

We really shouldn't ever halt with interrupts disabled.
Signed-off-by: Tony Luck <tony.luck@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: magnus.damm@gmail.com
Link: http://lkml.kernel.org/r/516d9a0c26048eae9c@agluck-desk.sc.intel.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/ia64/include/asm/irqflags.h

@@ -89,6 +89,7 @@ static inline bool arch_irqs_disabled(void)
 
 static inline void arch_safe_halt(void)
 {
+	arch_local_irq_enable();
 	ia64_pal_halt_light();	/* PAL_HALT_LIGHT */
 }