Change in coreboot[master]: cannonlake mainboards: Set PMC as hidden in devicetree

[Tim Wawrzynczak (Code Review)]

Attention is currently required from: Furquan Shaikh, Matt DeVillier, Jeremy Soller, Angel Pons, Karthik Ramasubramanian.
Tim Wawrzynczak has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/56008 )

Change subject: cannonlake mainboards: Set PMC as hidden in devicetree
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Patch Set 2:

(1 comment)

Patchset:

PS2:
> I wonder if we should set it for P2SB, too, then

```
src/mainboard/ocp/tiogapass/devicetree.cb:              device pci 1f.1 hidden end # p2sb
```

tiogapass apparently does!

The purpose would be if you have device callbacks you still want for the P2SB even though it's not enumerated