[PATCH] Export synchronize_irq on CONFIG_SMP=y

Currently, all arches which support SMP define synchronize_irq(irq)
to be a real function (generally defined in arch/$(ARCH)/kernel/irq.c).
This export was removed inadvertanly I believe in the "bit IRQ lock"
removal and IRQ cleanups ChangeSet.

arch/i386/kernel/i386_ksyms.c

@@ -132,6 +132,7 @@ EXPORT_SYMBOL_NOVERS(__write_lock_failed);
 EXPORT_SYMBOL_NOVERS(__read_lock_failed);
 
 /* Global SMP stuff */
+EXPORT_SYMBOL(synchronize_irq);
 EXPORT_SYMBOL(smp_call_function);
 
 /* TLB flushing */