hw/s390x/ipl: replace deprecated qdev_reset_all registration

hw/s390x/ipl: replace deprecated qdev_reset_all registration

Replace deprecated qdev_reset_all by resettable_cold_reset_fn for
the ipl registration in the main reset handlers.

This does not impact the behavior for the following reasons:
+ at this point resettable just call the old reset methods of devices
  and buses in the same order than qdev/qbus.
+ resettable handlers registered with qemu_register_reset are
  serialized; there is no interleaving.
+ eventual explicit calls to legacy reset API (device_reset or
  qdev/qbus_reset) inside this reset handler will not be masked out
  by resettable mechanism; they do not go through resettable api.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200123132823.1117486-12-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>