[$] Hardware-assisted Arm VMs for s390

A recentpatch set from Steffen Eiden and others has set the groundwork for allowinghardware-assisted emulation of Arm CPUs on s390 CPUs.Version two of the posting fixes a handful of smaller problems, but does notdiffer much.The patches were welcomedby the Arm maintainers, pending some discussion of how the collaboration between thearchitectures could be structured to prevent maintainability problems on the Armside. When those details are resolved, the patches could pave the way fortransparently running Arm-based virtual machines (VMs) on s390 hosts at native ornear-native speeds.