Also turn of teken for RB_MULTIPLE

RB_MULTIPLE without RB_SERIAL set is valid, and means 'Video first, then serial'
to the kernel (so kernel messages go to both, but /etc/rc uses video console
(this should be fixed, btw, but another day)). Check for RB_MULTIPLE as well as
RB_SERIAL where we want to to serial things. This means we'll use the old code
for emulation in these situations, which is likely best since we're outputing to
both and the old code is ligher weight allowing both to keep up w/o weird
scrolling things.