spapr: Reorganize CPU dt generation code

spapr: Reorganize CPU dt generation code

Reorganize CPU device tree generation code so that it be reused from
hotplug path. CPU dt entries are now generated from spapr_finalize_fdt()
instead of spapr_create_fdt_skel().

Note: This is how the split-up looks like now:

Boot path
---------
spapr_finalize_fdt
 spapr_populate_cpus_dt_node
  spapr_populate_cpu_dt
   spapr_fixup_cpu_numa_dt
   spapr_fixup_cpu_smt_dt

ibm,cas path
------------
spapr_h_cas_compose_response
 spapr_fixup_cpu_dt
  spapr_fixup_cpu_numa_dt
  spapr_fixup_cpu_smt_dt

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>