On a site note, the kernel will choose serial console on the Fuloong if the PMON variables novga and nokbd are both set (value does not matter), imitating what PMON does. To switch back to VGA console unset either of these variables in PMON and attach a USB keyboard.
BTW, testing this I think I found a bug. If either of novga or nokbd is set, the OpenBSD bootloader still displays its prompt on serial, but does not seem to get input from either serial or USB if a USB keyboard is attached. Only if I disconnect the USB keyboard, serial input starts to work. This is rather strange, and requires some more investigation. -Otto