[coreboot] v3 comments - was Serengeti vga hang

[ron minnich]

there is a phase 3 enable that enables a device (if needed) to appear
or disappear in config space. There is a phase 4 enable disable to
enable a device's resources to be read. Both of these usages appeared
in v2.

Sorry, I'm worn out (long day) if this makes no sense let me know.

ron