[S] Change in coreboot[master]: mb/google/myst: Enable variants for Myst

[Tim Van Patten (Code Review)]

Attention is currently required from: Raul Rangel, Jon Murphy, Karthik Ramasubramanian, Mark Hasemeyer.

Tim Van Patten has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74098 )

Change subject: mb/google/myst: Enable variants for Myst
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Patch Set 5:

(1 comment)

File src/mainboard/google/myst/mainboard.c:

https://review.coreboot.org/c/coreboot/+/74098/comment/49e6a6eb_d324e0bd 
PS4, Line 35: static void mainboard_enable(struct device *dev)
Do we need the rest from Skyrim?

```
    /* TODO: b/184678786 - Move into espi_config */
    /* Unmask eSPI IRQ 1 (Keyboard) */
    pm_write32(PM_ESPI_INTR_CTRL, PM_ESPI_DEV_INTR_MASK & ~(BIT(1)));
```

That bug references cezanne, but it was brought along for mendocino also.