[coreboot] thincan serial support

[ron minnich]

I need to do ttl to rs232 for the thincan. I am thinking of a cook
book procedure so others can do this easily.

The first ingredient is this: http://www.superdroidrobots.com/rs232.htm

Anyone have a better choice? I like this as it comes with schematics
and howto. From here I should be able
to do a simple "howto" writeup.

CS5536 doesn't have USB debug port support :-(, so this is the best
choice. We're going to need a Kconfig
option on v3 for enabling serial over DDC on boards using cs5536.

thanks

ron