Fix arm build of drivers/xen/events/

The merge of irq-core-for-linus branch broke it.
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Merge tag 'stable/for-linus-3.15-tag2' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull Xen build fix from David Vrabel:
 "Fix arm build of drivers/xen/events/

  The merge of irq-core-for-linus branch broke it"

* tag 'stable/for-linus-3.15-tag2' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  Xen: do hv callback accounting only on x86

drivers/xen/events/events_base.c

@@ -1248,8 +1248,8 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 	irq_enter();
 #ifdef CONFIG_X86
 	exit_idle();
-#endif
 	inc_irq_stat(irq_hv_callback_count);
+#endif
 
 	__xen_evtchn_do_upcall();