The -device switch is the users frontend to the qdev_device_add function
added by the previous patch.

Also adds a linked list where command line options can be saved.
Use it for the new -device and for the -usbdevice and -bt switches.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>