[M] Change in coreboot[master]: mb/google/myst: Enable AP <-> GSC communication

[Mark Hasemeyer (Code Review)]

Attention is currently required from: Raul Rangel, Jon Murphy, Tim Van Patten, Karthik Ramasubramanian.

Mark Hasemeyer has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74111 )

Change subject: mb/google/myst: Enable AP <-> GSC communication
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Patch Set 5:

(1 comment)

File src/mainboard/google/myst/variants/baseboard/gpio.c:

https://review.coreboot.org/c/coreboot/+/74111/comment/8421841e_78704ef6 
PS5, Line 182: 	PAD_INT(GPIO_18, PULL_NONE, EDGE_LOW, STATUS_DELIVERY),
Doh! Missed this one too: GPIO_84

Also wondering if it makes sense to redefine everything that was defined here:
https://review.coreboot.org/c/coreboot/+/74095/4/src/mainboard/google/myst/v...

It seems like pins and bus numbers get redefined in numerous places. It would be nice to cut down on that.