spapr_rtas: Abstract rtas_start_cpu() with qemu_get_cpu()

Instead of looping over all CPUArchState, use a helper to obtain the
desired CPUState.
Free the "cpu" variable for PowerPCCPU, to access its CPUPPCState.
Signed-off-by: NAndreas Färber <afaerber@suse.de>

hw/ppc/spapr_rtas.c

@@ -160,8 +160,7 @@ static void rtas_start_cpu(sPAPREnvironment *spapr,
                            uint32_t nret, target_ulong rets)
 {
     target_ulong id, start, r3;
-    CPUState *cpu;
-    CPUPPCState *env;
+    CPUState *cs;
 
     if (nargs != 3 || nret != 1) {
         rtas_st(rets, 0, -3);
@@ -172,14 +171,12 @@ static void rtas_start_cpu(sPAPREnvironment *spapr,
     start = rtas_ld(args, 1);
     r3 = rtas_ld(args, 2);
 
-    for (env = first_cpu; env; env = env->next_cpu) {
-        cpu = CPU(ppc_env_get_cpu(env));
-
-        if (cpu->cpu_index != id) {
-            continue;
-        }
+    cs = qemu_get_cpu(id);
+    if (cs != NULL) {
+        PowerPCCPU *cpu = POWERPC_CPU(cs);
+        CPUPPCState *env = &cpu->env;
 
-        if (!cpu->halted) {
+        if (!cs->halted) {
             rtas_st(rets, 0, -1);
             return;
         }
@@ -192,9 +189,9 @@ static void rtas_start_cpu(sPAPREnvironment *spapr,
         env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
         env->nip = start;
         env->gpr[3] = r3;
-        cpu->halted = 0;
+        cs->halted = 0;
 
-        qemu_cpu_kick(cpu);
+        qemu_cpu_kick(cs);
 
         rtas_st(rets, 0, 0);
         return;