[S] Change in coreboot[main]: soc/amd/phoenix: Add build rules to enable CBFS verification

[Martin L Roth (Code Review)]

Attention is currently required from: Felix Held, Fred Reitberger, Jason Glenesk, Jon Murphy, Karthik Ramasubramanian, Matt DeVillier.

Martin L Roth has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/78233?usp=email )

Change subject: soc/amd/phoenix: Add build rules to enable CBFS verification
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Patch Set 2:

(2 comments)

File src/soc/amd/phoenix/Makefile.inc:

https://review.coreboot.org/c/coreboot/+/78233/comment/01287176_150e7975 :
PS2, Line 49: # 0x80 accounts for the cbfs_file struct + filename + metadata structs, aligned to 64 bytes
            : # Building the cbfs image will fail if the offset isn't large enough
            : AMD_FW_AB_POSITION := 0x80
Should we change this for all platforms AMD by checking if cbfs verification is enabled?

https://review.coreboot.org/c/coreboot/+/78233/comment/42cd130a_b51920f4 :
PS2, Line 346: 
Do we need to add the key signature block as well, or is that already done by default?