util/kconfig: Stop trying to make sense of Linux configs

It only leads to missing symbol errors.

Change-Id: Idbce93232ba2b54561abab5b2747c418d6efa92b
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56373
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: Lean Sheng Tan <lean.sheng.tan@intel.com>
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/util/kconfig/Makefile.inc b/util/kconfig/Makefile.inc
index db8b1be..bedb41d 100644
--- a/util/kconfig/Makefile.inc
+++ b/util/kconfig/Makefile.inc
@@ -24,6 +24,7 @@
 kecho := echo
 
 -include $(objk)/Makefile.real
+unexport KCONFIG_DEFCONFIG_LIST
 
 # Fill in Linux kconfig build rules to work