[M] Change in coreboot[master]: soc/intel/common/block/pcie/rtd3: Add root port mutex support

[Cliff Huang (Code Review)]

Attention is currently required from: Hannah Williams, Anil Kumar K, Tarun Tuli, Angel Pons, Maximilian Brune.

Cliff Huang has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/73380 )

Change subject: soc/intel/common/block/pcie/rtd3: Add root port mutex support
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Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/73380/comment/59807dab_edb59cc5 
PS2, Line 23: BRANCH=firmware-brya-14505.B
> Is there a corresponding bug that goes with this?

There is no direct bug, but the need of this mutex was observed while I was working on 241850118, where one case is doing WWAN reset and S0ix.