xen/xsm: Split vm_event_op into three separate labels

xen/xsm: Split vm_event_op into three separate labels

The XSM label vm_event_op has been used to control the three memops
controlling mem_access, mem_paging and mem_sharing. While these systems
rely on vm_event, these are not vm_event operations themselves. Thus,
in this patch we introduce three separate labels for each of these memops.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Tim Deegan <tim@xen.org>