Suspend is not supported on ARM64 for the moment.
Modified to check for ARM instead of !x86, since ARM is where support is
missing. Other Xen architectures might get suspend support sooner.
Submitted by: Elliott Mitchell <ehem+freebsd@m5p.com>
Original implementation: Julien Grall <julien@xen.org>, 2014-01-13 17:41:15