Functionally it is a recursive qom-list with qom-get per non-child<>
property. Some failures needed to be handled, such as trying to read a
pointer property, which is not representable in QMP. Those print a
literal "<EXCEPTION>".

Tested-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>