The structure, introduced in cfa0b7b82fbdda56d7160569def5c6133eb045aa,
is needed on all Xen architectures and should not be in the x86 area.
As ARM only has the PVv2/PVH version, leave the PVv1 version as
x86-only.
---
CHECK: Is copyright notice correct? Since this originated in
cfa0b7b82fbdda56d7160569def5c6133eb045aa, likely Citrix owns copyright,
but the notice wasn't updated then.