qdev: Simplify the SysBusDeviceClass::init path

qdev: Simplify the SysBusDeviceClass::init path

Instead of using
  SysBusDeviceClass::realize
   -> DeviceClass::realize
       -> DeviceClass::init
           -> sysbus_device_init
              -> SysBusDeviceClass::init

Simplify the path by directly calling SysBusDeviceClass::init
in SysBusDeviceClass::realize:

  SysBusDeviceClass::realize
   -> SysBusDeviceClass::init

Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <20180419212727[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
[Removal of DeviceClass::init() moved into next patch,
sysbus_realize() tweaked for clarity]
Signed-off-by: Markus Armbruster <[email protected]>
Message-Id: <20180528144509[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>