[S] Change in coreboot[main]: drivers/option: Add CBFS file based option backend

[Subrata Banik (Code Review)]

Attention is currently required from: Julius Werner, Nicholas Chin.

Subrata Banik has posted comments on this change by Nicholas Chin. ( https://review.coreboot.org/c/coreboot/+/85905?usp=email )

Change subject: drivers/option: Add CBFS file based option backend
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Patch Set 4:

(1 comment)

Patchset:

PS4:
> Is this just so that socs and mainboards can select this as a default rather than the current OPTION_BACKEND_NONE? The CBFS file option backend should always be available since the availability of cbfs files is an integral part of coreboot and can always be manually selected in the config.

`USE_CBFS_FILE_OPTION_BACKEND` is part of the choice so, SoC/mainboard won't be able to select `USE_CBFS_FILE_OPTION_BACKEND` directly. Therefore, we need HAVE_CBFS_FILE_OPTION_BACKEND to allow controlling `USE_CBFS_FILE_OPTION_BACKEND`. Later SoC//mainboard can easily select HAVE_CBFS_FILE_OPTION_BACKEND.