* split the old SysBus init function into an instance_init
  and a Device realize function
* use DeviceClass::realize instead of SysBusDeviceClass::init
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: Nxiaoqiang zhao <zxq_yx_007@163.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>