Help was shoehorned into device creation, qdev_device_add(). Since
help doesn't create a device, it returns NULL, which looks to callers
just like failed device creation. Monitor handler do_device_add()
doesn't care, but main() exits unsuccessfully.
Move help out of device creation, into new qdev_device_help().
Signed-off-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>