ICH9 is a south bridge which doesn't necessarily depend on x86, so move
it into the southbridge folder, analoguous to PIIX.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230213173033.98762-13-shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>