[whoops, this didn't make it to port-pmax the first time]

hi all, 

I've committed another batch of merges of the scc driver.
I've verified they work on a pmax and stared very hard at the
results (before and after changes) after C preprocessing.
I don't _think_ I broke anything, but if console or serial 
code breaks on TC alphas tomorrow, it's probably my fault.

As usual, send a PR if anything breaks.

PS: the dialin/dialout changes discussed on tech-kern got committed
just before.  If you're using scc ports for dialout, be *very* careful
to setup dialout devices and use them!