Copy x86 VDSO code to AArch64

While it duplicates hundreds of lines of code, this is the
short term strategy Cyrill and I have agreed to for supporting
VDSOs across multiple architectures [1]. With better
understanding of where things differ per-architecture, or even
improved consolidation in the kernel, we can hopefully move to
a more shared implementation in the future.

1. http://lists.openvz.org/pipermail/criu/2014-August/015218.html



Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>