[L] Change in coreboot[master]: screebo: initial coreboot for rex variant

[Simon Zhou (Code Review)]

Attention is currently required from: YH Lin, Tarun Tuli, Subrata Banik, Kapil Porwal.

Simon Zhou has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74392 )

Change subject: screebo: initial coreboot for rex variant
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Patch Set 2:

(1 comment)

Patchset:

PS2:
> @Simon, do u have platform mapping document for Screebo? which we can refer to review the code?

Yes, we will update the hardware configuration at later change. this change is only for AP firmware creation.