target-ppc: Enable PMU SPRs migration

This enabled PMU SPRs migration by hooking hypv privileged versions with
"KVM one reg" IDs.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
