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

[Julius Werner (Code Review)]

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

Julius Werner 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)

Patchset:

PS2: 
I may be forgetting some details here, but wasn't returning UNDEFINED_FW_CONFIG (i.e. 0xffffffffffffffff) when the config has not been set an intentional feature of the FW_CONFIG design? It sets every bit to 1 so that every device will try to probe. I think(?) that was intended for the first factory boot, so that the machine is bootable before the point where it has time to program the right FW_CONFIG value into CBI.