In latest linux-next the vdso zone is placed _after_ vvar
zone so eventually we need to handle any combination of
the following cases

 - no vvar zone
 - vvar before vdso
 - vvar after vdso

Here we address all them.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>