Introduce type constant and cast macro and enforce its use by
renaming A9MPPrivState::busdev field to parent_obj.
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andreas Färber <andreas.faerber@web.de>
