xen/control: disable 15226522304868a8312a84f8ff549fdc6bbf54db on !x86

[ehem_freebsd_m5p.com]

Summary

Commit 15226522304868a8312a84f8ff549fdc6bbf54db was implemented strictly
for x86. Unfortunately one of the pieces was mixed into a common area
breaking other architectures. For now disable these bits on !x86, this
should be cleaned up later.

[royger]

I'm fine with this, if in the future other arches require some arch specific stuff to be executed at a similar place we could introduce an arch-specific hook (ie: xen_cpu_resumed or some such, I'm bad at naming).

[ehem_freebsd_m5p.com]

Then what I realized D29599 heavily overlaps with this. I suspect I was trying to see whether xctrl_suspend() could be made to build on ARM and found this spot was particularly problematic. When you're shuffling 82 patches around you can lose track of overlapping ones.