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

[build bot (Jenkins) (Code Review)]

build bot (Jenkins) has posted comments on this change. ( https://review.coreboot.org/21288 )

Change subject: ifdtool: optimize some code and data type
......................................................................

Patch Set 7:

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/14914/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/59634/ : SUCCESS