[S] Change in coreboot[main]: src/lib: Add Kconfig variable for fw_config default value

[Cliff Huang (Code Review)]

Attention is currently required from: Anil Kumar K, Bora Guvendik, Subrata Banik, Wonkyu Kim.

Cliff Huang has posted comments on this change by Cliff Huang. ( https://review.coreboot.org/c/coreboot/+/83153?usp=email )

Change subject: src/lib: Add Kconfig variable for fw_config default value
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Patch Set 2:

(1 comment)

File src/Kconfig:

https://review.coreboot.org/c/coreboot/+/83153/comment/34df8c9b_d20df773?usp... :
PS2, Line 548: 0x00000
> unable to follow the motivation. […]

Good point! This is used in make build environment where no CBI value is synced from config.star. Also, with this flag been overridden in config.<board>, the different fw_config value can be tested while it is not provided from Chrome EC and VPD. For instance, in simulation environment, the targeted overridden value can be used with the need of updating the value in the storage model prior to boot.