Change in coreboot[master]: amd/stoneyridge: Add uart.c to smm-y list

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Change subject: amd/stoneyridge: Add uart.c to smm-y list
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Patch Set 2:

Build Successful

https://qa.coreboot.org/job/coreboot-gerrit/61316/ : SUCCESS

https://qa.coreboot.org/job/coreboot-checkpatch/16463/ : SUCCESS