xen/events: move 2-level specific code into its own file

In preparation for alternative event channel ABIs, move all the
functions accessing the shared data structures into their own file.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
diff --git a/include/xen/events.h b/include/xen/events.h
index c9ea10e..32ae0f2 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -73,6 +73,8 @@
 
 /* Determine the IRQ which is bound to an event channel */
 unsigned irq_from_evtchn(unsigned int evtchn);
+int irq_from_virq(unsigned int cpu, unsigned int virq);
+unsigned int evtchn_from_irq(unsigned irq);
 
 /* Xen HVM evtchn vector callback */
 void xen_hvm_callback_vector(void);