hw/s390x: Fix crash that occurs when inspecting older versioned machines types

hw/s390x: Fix crash that occurs when inspecting older versioned machines types

qemu-system-s390x currently crashes when trying to inspect older
machines types, for example:

 $ echo '{ "execute": "qmp_capabilities" }
         { "execute": "qom-list-properties","arguments":
           { "typename": "s390-ccw-virtio-3.0-machine"}}' \
   | ./qemu-system-s390x -qmp stdio -no-shutdown
 {"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major": 9},
  "package": "v9.2.0-1071-g81e97df3e7"}, "capabilities": ["oob"]}}
 {"return": {}}
 **
 Bail out! ERROR:../target/s390x/cpu_models.c:832:s390_set_qemu_cpu_model:
  assertion failed: (QTAILQ_EMPTY_RCU(&cpus_queue))
 Aborted (core dumped)

The problem is that the versioned s390-ccw-virtio machine types
use instance_init() to set global state that should be initialized
before the CPUs get instantiated. But instance_init() is not called
only for the machine that is finally used, it is also called for
temporary instances of objects that are e.g. just created for
introspection. That means that those instance_init() functions can
also be called while a machine (and its CPUs) is already created,
which triggers the assertion in cpu_models.c.

So we must not use instance_init() for setting global state, but
use the machine->init() function instead, which is really only called
once when the machine comes to life.

Fixes: 3b00f702c2 ("s390x/cpumodel: add zpci, aen and ais facilities")
Message-ID: <20250120085059.239345-1-thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>