vl: add -object option to create QOM objects from the command line

This will create a new QOM object in the '/objects' path.  Note that properties
are set in order which allows for simple objects to be initialized entirely
with this option and then realized.

This option is roughly equivalent to -device but for things that are not
devices.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
