[S] Change in coreboot[master]: mb/{skl,kbl}: Use true/false macros for eist_enable dt option

[Felix Singer (Code Review)]

Felix Singer has abandoned this change. ( https://review.coreboot.org/c/coreboot/+/75965?usp=email )

Change subject: mb/{skl,kbl}: Use true/false macros for eist_enable dt option
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Abandoned

Covered by CB:75888 now.