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 --cc drivers/xen/events/Makefile
Simple merge

diff --cc drivers/xen/events/events_2l.c
Simple merge

diff --cc drivers/xen/events/events_base.c
Simple merge

diff --cc drivers/xen/events/events_internal.h
Simple merge

diff --cc include/xen/events.h
Simple merge