spapr: add "stop-self" RTAS call required to support hot CPU unplug

PAPR+ requires two RTAS calls to be supported by the hypervisor in
order to allow hotplugging VCPUs from the guest. The "start-cpu" RTAS
call was already there but "stop-self" was not.

This adds the "stop-self" RTAS call.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>
PPC: spapr: iommu: rework traces

This converts old style fprintf to traces.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[agraf: change patch subject]
Signed-off-by: Alexander Graf <agraf@suse.de>