This source file implements a stellaris gamepad device; rename
it so that it is a closer match to the device name.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20231030114802.3671871-2-peter.maydell@linaro.org