pnv_core: Allocate cpu thread objects individually

Currently, we allocate space for all the cpu objects within a single core
in one big block.  This was copied from an older version of the spapr code
and requires some ugly pointer manipulation to extract the individual
objects.

This design was due to a misunderstanding of qemu lifetime conventions and
has already been changed in spapr (in 94ad93bd "spapr_cpu_core: instantiate
CPUs separately".

Make an equivalent change in pnv_core to get rid of the nasty pointer
arithmetic.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>

include/hw/ppc/pnv_core.h

@@ -34,7 +34,7 @@ typedef struct PnvCore {
     CPUCore parent_obj;
 
     /*< public >*/
-    void *threads;
+    PowerPCCPU **threads;
     uint32_t pir;
 
     MemoryRegion xscom_regs;