Change in coreboot[master]: lenovo/x230: introduce FHD variant

[Nico Huber (Code Review)]

Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/28950 )

Change subject: lenovo/x230: introduce FHD variant
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Patch Set 8:
> I've published the schematic of the latest adapter board here: https://nitrocaster.me/files/X230U_rev6_schematic.pdf
> Hopefully this will help getting this merged.
> Let me know what you guys think.

Thanks for sharing! It answers some questions and raises new :)

Most of all, I wonder what exactly U1 does and if it is necessary
at all if one controls the firmware. Is it simply translating the
BL_CTL_SYS signal to a different PWM frequency? or is it also
needed as a buffer? Also, what frequency does it expect on
BL_CTL_SYS, if any specific?

And, can you confirm that:
* With the default assembly, one can't control panel power via software.
* But by moving F1 to J1, it would become possible?