Change in coreboot[master]: soc/amd/stoneyridge: Add XHCI PM register access functions

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Change subject: soc/amd/stoneyridge: Add XHCI PM register access functions
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Patch Set 3:

Build Successful

https://qa.coreboot.org/job/coreboot-gerrit/64168/ : SUCCESS

https://qa.coreboot.org/job/coreboot-checkpatch/18998/ : SUCCESS