spapr: fix missing CPU core nodes in DT when running with TCG

Commit 5d0fb1508e "spapr: consolidate the VCPU id numbering logic
in a single place" introduced a helper to detect thread0 of a virtual
core based on its VCPU id. This is used to create CPU core nodes in
the DT, but it is broken in TCG.

$ qemu-system-ppc64 -nographic -accel tcg -machine dumpdtb=dtb.bin \
                    -smp cores=16,maxcpus=16,threads=1
$ dtc -f -O dts dtb.bin | grep POWER8
                PowerPC,POWER8@0 {
                PowerPC,POWER8@8 {

instead of the expected 16 cores that we get with KVM:

$ dtc -f -O dts dtb.bin | grep POWER8
                PowerPC,POWER8@0 {
                PowerPC,POWER8@8 {
                PowerPC,POWER8@10 {
                PowerPC,POWER8@18 {
                PowerPC,POWER8@20 {
                PowerPC,POWER8@28 {
                PowerPC,POWER8@30 {
                PowerPC,POWER8@38 {
                PowerPC,POWER8@40 {
                PowerPC,POWER8@48 {
                PowerPC,POWER8@50 {
                PowerPC,POWER8@58 {
                PowerPC,POWER8@60 {
                PowerPC,POWER8@68 {
                PowerPC,POWER8@70 {
                PowerPC,POWER8@78 {

This happens because spapr_get_vcpu_id() maps VCPU ids to
cs->cpu_index in TCG mode. This confuses the code in
spapr_is_thread0_in_vcore(), since it assumes thread0 VCPU
ids to have a spapr->vsmt spacing.

    spapr_get_vcpu_id(cpu) % spapr->vsmt == 0

Actually, there's no real reason to expose cs->cpu_index instead
of the VCPU id, since we also generate it with TCG. Also we already
set it explicitly in spapr_set_vcpu_id(), so there's no real reason
either to call kvm_arch_vcpu_id() with KVM.

This patch unifies spapr_get_vcpu_id() to always return the computed
VCPU id both in TCG and KVM. This is one step forward towards KVM<->TCG
migration.

Fixes: 5d0fb1508e
Reported-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -3810,13 +3810,7 @@ static void spapr_pic_print_info(InterruptStatsProvider *obj,
 
 int spapr_get_vcpu_id(PowerPCCPU *cpu)
 {
-    CPUState *cs = CPU(cpu);
-
-    if (kvm_enabled()) {
-        return kvm_arch_vcpu_id(cs);
-    } else {
-        return cs->cpu_index;
-    }
+    return cpu->vcpu_id;
 }
 
 void spapr_set_vcpu_id(PowerPCCPU *cpu, int cpu_index, Error **errp)