[PATCH] IPI calltraces on x86_64

This patch makes x86_64 kernel to print calltraces on _all_
CPUs on Alt-SysRq-p and NMI LOCKUP.
This patch supplements the one made for i386
some time ago and included in -mm tree.
Since it proved its usefullness many times already
we did the same patch for x86_64.

Signed-Off-By: Pavel Emelianov <xemul@openvz.org>
Signed-Off-By: Kirill Korotaev <dev@openvz.org>