spapr: Rework spapr_fixup_cpu_dt()

spapr: Rework spapr_fixup_cpu_dt()

In PPC code we usually use the "cs" name for a CPUState* variables
and "cpu" for PowerPCCPU. So let's change spapr_fixup_cpu_dt() to
use same rules as spapr_create_fdt_skel() does.

This adds missing nodes creation if they do not already exist in
the current device tree, this is going to be used from
the client-architecture-support handler.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>