Change in coreboot[master]: [WIP/UNTESTED]nb/intel/x4x: Implement both read and write training

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Change subject: [WIP/UNTESTED]nb/intel/x4x: Implement both read and write training
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Patch Set 2: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/17925/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/62961/ : SUCCESS