[M] Change in coreboot[main]: drivers/intel/fsp2_0: Add early low-battery shutdown during memory init

[Subrata Banik (Code Review)]

Attention is currently required from: Andrey Petrov, Intel coreboot Reviewers, Julius Werner, Jérémy Compostella, Karthik Ramasubramanian, Ronak Kanabar.

Subrata Banik has posted comments on this change by Subrata Banik. ( https://review.coreboot.org/c/coreboot/+/86452?usp=email )

Change subject: drivers/intel/fsp2_0: Add early low-battery shutdown during memory init
......................................................................

Patch Set 6:

(2 comments)

File src/drivers/intel/fsp2_0/memory_init.c:

https://review.coreboot.org/c/coreboot/+/86452/comment/7cf31de7_7450ae5f?usp... :
PS6, Line 352: do_low_battery_poweroff
> No, I am suggesting setting the `__noreturn` attribute on the function that should not return.
> modified   src/include/halt.h
> @@ -12,6 +12,6 @@ static inline __noreturn void halt(void)
>  }
>
>  /* Power off the system. */
> -void poweroff(void);
> +void __noreturn poweroff(void);
>
>  #endif /* __HALT_H__ */
> modified   src/soc/intel/common/reset.h
> @@ -30,6 +30,6 @@ efi_return_status_t fsp_get_pch_reset_status(void);
>   *
>   * Call this function to power off the platform if the battery level is critically low.
>   */
> -void do_low_battery_poweroff(void);
> +void __noreturn do_low_battery_poweroff(void);
>
>  #endif	/* _INTEL_COMMON_RESET_H_ */
>
> Your code could look like this:
> /* User has been notified of low battery; safe to power off. */
> if (CONFIG(MAINBOARD_HAS_EARLY_LIBGFXINIT)) {
>         platform_display_early_shutdown_notification(NULL);
>         do_low_battery_poweroff(); /* Do not return */
> }
>
> /* Defer shutdown until FSP-M (uGOP) display text message for user notification */
> platform_display_early_shutdown_notification(fspm_upd);
> *defer_shutdown = true;

I have accommodated your feedback in CB:86578 and don't feel that we need to modify poweroff w/ `__noreturn` because adding halt() inside do_low_battery_poweroff API is enough to ensure that return type is non-return (to avoid compilation error).

```
static inline __noreturn void halt(void)
{
    abort();
}
```

https://review.coreboot.org/c/coreboot/+/86452/comment/ef1c731b_1a47dcf5?usp... :
PS6, Line 367: defer_shutdown_in_low_battery_boot
> what about `poweroff_after_fsp_execution` ?

Acknowledged