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/drivers/xen/events/Makefile b/drivers/xen/events/Makefile
index f0bc607..08179fe 100644
--- a/drivers/xen/events/Makefile
+++ b/drivers/xen/events/Makefile
@@ -1,3 +1,4 @@
 obj-y += events.o
 
 events-y += events_base.o
+events-y += events_2l.o