Update romstage.c

NB: most of the code is a copy from ibase/mb899/romstage.c 
probably I have to find another board like mine...

anyway, now The serial do not work anymore...
(it works just when I flash the rom and ask for reboot, I can see a msg : "setting up static southbridge register ..." and no thing happen!
the board do not reboot.
when I reboot it by hand, there is no msg on serial )