Change in coreboot[master]: stage_cache: Add resume_from_stage_cache()

[Kyösti Mälkki (Code Review)]

Attention is currently required from: Jason Glenesk, Raul Rangel, Lee Leahy, Marshall Dawson, Angel Pons, Huang Jin, Andrey Petrov, Patrick Rudolph, Felix Held.
Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/50000 )

Change subject: stage_cache: Add resume_from_stage_cache()
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Patch Set 1:

(1 comment)

File src/lib/prog_loaders.c:

https://review.coreboot.org/c/coreboot/+/50000/comment/c071fbd6_ebc56c93 
PS1, Line 118: 	if (resume_from_stage_cache())
> Where did the ENV_X86 guard go? Should the comment above be updated?

If we did have !ENV_X86 with HAVE_ACPI_RESUME and !NO_STAGE_CACHE it should be fine to resume from stage cache, right.

I am not sure where the work Julius does with CBFS per-file hashing leads us. Will these somehow converge such that verification step already leaves the copy we want inside the stage cache and the test of acpi_is_wakeup_s3() would be dropped.