Add support for arm64_linux26

Add support for arm64_linux26

Add support for the arm64/aarch64 architecture on Linux 2.6+. The
param header file is mostly combined from arm and amd64.

Note that the code for syscall interception has not been updated for
arm64, so this will not build on arm64 without support for kernel
keyrings. This also does not define any AFS syscall number, since no
number in the Linux arm64 syscall table is "free" for us to use, as
far as I am aware.

Adapted from initial patches from Micheal Waltz <mwaltz@qualcomm.com>.

Reviewed-on: https://gerrit.openafs.org/11940
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 4f7550dcaf9375046514cdd97cea0f667e955e9f)

Change-Id: I12988da1fbbc7e3733fddf4ca11ad65b96a9c02f
Reviewed-on: https://gerrit.openafs.org/13095
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>