xen: add rebind_evtchn_irq

Add rebind_evtchn_irq(), which will rebind an device driver's existing
irq to a new event channel on restore.  Since the new event channel
will be masked and bound to vcpu0, we update the state accordingly and
unmask the irq once everything is set up.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/xen/events.h b/include/xen/events.h
index acd8e06..a82ec0c 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -32,6 +32,7 @@
 
 void xen_send_IPI_one(unsigned int cpu, enum ipi_vector vector);
 int resend_irq_on_evtchn(unsigned int irq);
+void rebind_evtchn_irq(int evtchn, int irq);
 
 static inline void notify_remote_via_evtchn(int port)
 {