Extract generic ioport_fuzz_qtest() method from
i440fx_fuzz_qtest(). This will help to write tests
not specific to the i440FX controller.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200514143433.18569-7-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>