[S] Change in coreboot[main]: soc/intel/cmn/pmc: Add support for early power off

[Jérémy Compostella (Code Review)]

Attention is currently required from: Intel coreboot Reviewers, Julius Werner, Karthik Ramasubramanian, Subrata Banik.

Jérémy Compostella has posted comments on this change by Subrata Banik. ( https://review.coreboot.org/c/coreboot/+/86336?usp=email )

Change subject: soc/intel/cmn/pmc: Add support for early power off
......................................................................

Patch Set 3:

(1 comment)

File src/soc/intel/common/block/pmc/pmclib.c:

https://review.coreboot.org/c/coreboot/+/86336/comment/88873401_4439f76d?usp... :
PS3, Line 635: __weak void platform_do_early_poweroff(void)
The `pmc.c` file is intended to be a generic module, primarily interacting with PMC-related APIs. Including any calls to Chrome EC-specific functions appears inappropriate within this context. The objective is to assign the early power-off sequence management to the Embedded Controller (EC), and it is suggested that the weak function mechanism be utilized directly for this purpose, rather than introducing an indirect call within `pmclib.c`.

Additionally, scalability should be considered. For instance, if a different vendor desires to implement their own early shutdown process, the current design would necessitate further modifications to the `pmclib.c` file.
> Calling pmc_control_poweroff in the early stage doesn't add any value. system might eventually hang in S0 with display being off and system burn all fuels w/o any meaningful purpose.

In my opinion, the goal is twofold:

1.  Maintaining the default behavior when no specific early shutdown routine is provided. This approach allows platforms that do not require specialized early shutdown management to operate as intended.
2.  Including a disclaimer to indicate that the generic PMC solution may not be effective.