Change in coreboot[master]: ifdtool: optimize some code and data type

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Change subject: ifdtool: optimize some code and data type
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Patch Set 9: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/14917/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/59637/ : SUCCESS