x86: Extend validity of bsp_to_cpu

As we hard-wire the BSP to CPU 0 anyway and cpuid_apic_id equals
cpu_index, bsp_to_cpu can also be based on the latter directly. This
will help an early user of it: KVM while initializing mp_state.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

hw/pc.c

@@ -760,7 +760,8 @@ static void pc_init_ne2k_isa(NICInfo *nd)
 
 int cpu_is_bsp(CPUState *env)
 {
-    return env->cpuid_apic_id == 0;
+    /* We hard-wire the BSP to the first CPU. */
+    return env->cpu_index == 0;
 }
 
 static CPUState *pc_new_cpu(const char *cpu_model)