[M] Change in coreboot[main]: vc/google/chromeos: Implement platform callback for critical shutdown

[Julius Werner (Code Review)]

Attention is currently required from: Karthik Ramasubramanian, Subrata Banik.

Julius Werner has posted comments on this change by Subrata Banik. ( https://review.coreboot.org/c/coreboot/+/86228?usp=email )

Change subject: vc/google/chromeos: Implement platform callback for critical shutdown
......................................................................

Patch Set 7:

(1 comment)

File src/vendorcode/google/chromeos/battery.c:

https://review.coreboot.org/c/coreboot/+/86228/comment/d9e36e45_05dc603b?usp... :
PS7, Line 59: 	google_chromeec_reboot(EC_REBOOT_COLD_AP_OFF, 0);
> > I'm still not really clear why this needs to be an EC command rather than a normal `poweroff()`? I […]

Well then, like I said, I think the better solution would be to make sure the `poweroff()` function implemented by the platform does the right thing, rather than forcing platform-independent code to deal with this quirk.

For example, you could add something like this to the top of the `poweroff()` implementation in `intel/common/block/pmc/pmclib.c`:
```
if (ENV_ROMSTAGE_OR_BEFORE) {
  platform_do_intel_early_poweroff();
} else {
  pmc_enable_...
  if (!ENV_SMM)
    halt();
}
```
and then elsewhere in that file
```
__weak void platform_do_intel_early_poweroff(void) {
  printk(BIOS_EMERG, "This platform doesn't know how to power off before ramstage, hanging!\n");
  halt();
}
```
and then somewhere in `vendorcode/google/chromeos` you can override that function (in a file that gets compiled for Intel platforms when CONFIG_EC_GOOGLE_CHROMEEC is set)
```
void platform_do_intel_early_poweroff(void) {
  google_chromeec_reboot(EC_REBOOT_COLD_AP_OFF, 0);
  halt();
}
```
And then other parts of coreboot can just call `poweroff()` whenever they need to power off the system without having to know about these platform-specific quirks.