Drop the old Sysbus init and use instance_init and
DeviceClass::realize instead

Signed-off-by: xiaoqiang zhao <zxq_yx_007@163.com>
Message-id: 20161023091816.3839-3-zxq_yx_007@163.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>