xen/irq: Export 'xen_pirq_from_irq' function.

We need this to find the real Xen PIRQ value for a device
that requests an MSI or MSI-X. In the past we used
'xen_gsi_from_irq' since that function would return
an Xen PIRQ or GSI depending on the provided IRQ. Now that
we have seperated that we need to use the correct
function.

[v2: Deal with rebase on stable/irq.cleanup]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events.c

@@ -763,6 +763,12 @@ out:
 	return irq;
 }
 
+
+int xen_pirq_from_irq(unsigned irq)
+{
+	return pirq_from_irq(irq);
+}
+EXPORT_SYMBOL_GPL(xen_pirq_from_irq);
 int bind_evtchn_to_irq(unsigned int evtchn)
 {
 	int irq;

include/xen/events.h

@@ -95,6 +95,9 @@ int xen_destroy_irq(int irq);
 /* Return irq from pirq */
 int xen_irq_from_pirq(unsigned pirq);
 
+/* Return the pirq allocated to the irq. */
+int xen_pirq_from_irq(unsigned irq);
+
 /* Determine whether to ignore this IRQ if it is passed to a guest. */
 int xen_test_irq_shared(int irq);