Option C with GPLv2+ licensing.
A few quick things:
SUPERIO_FINTEK_F81865F_HAS_EARLY_SERIAL seems long-winded for a name.
I prefer to define CONFIG_SUPERIO_HAS_EARLY_SERIAL (or even just CONFIG_HAS_EARLY_SERIAL) within the superio Kconfig and not in mainboard Kconfig. This I think would be a per-superio setting. While we're at it, have we seen a board with 2+ superios?
Having said that though, isn't early serial support sort of mandatory anyway?
Secretly I'm hoping that some of my ideas end up in here. :-)
Cheers Keith