[XS] Change in coreboot[master]: mb/google/rex: enable d3hot for storage devices

[Sukumar Ghorai (Code Review)]

Attention is currently required from: Eric Lai, Jakub Czapiga, Kangheui Won, Kapil Porwal, Subrata Banik, Tarun Tuli.

Sukumar Ghorai has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/76835?usp=email )

Change subject: mb/google/rex: enable d3hot for storage devices
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Patch Set 3:

(1 comment)

Patchset:

PS2:
> d3hot or d3cold here? will this effect another SSD?

d3hot
Rex and screebo using Micron (MTFDKBA512TFK & MTFDKBA512QFM respectively), these SSD having lower snoon/non-snoop LTRs (~5ms) and blocking S0i2.2 entry in MTL. Hence we need this feature (d3hot) as altername power management to avoid the Link state powermanager(as today). i.e. required for all SSD having lower LTR and blocking S0i2.2
Do to suggest to sane changes for all varients?