vdso: Add vdso_put_mark helper

Instead of opencoded mark injection provide
a helper for easier grepability.

[xemul: Go ahead and remove the INIT_VDSO_MARK at all]

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
vdso: No need to fetch pfn if marked vdso area has been met

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>