buildman and #include config fragments are difficult to work with

When working with defconfig files such as configs/j721e_sk_a72_defconfig the need to duplicate information such as:

CONFIG_ARM=y
CONFIG_ARCH_K3=y
CONFIG_SOC_K3_J721E=y
CONFIG_TARGET_J721E_A72_EVM=y

For the sake of buildman being able to invoke and build correctly makes creation of new defconfigs that use the #include mechanism to avoid duplication difficult to understand the required process. Ideally, we need some way to know that we need to either invoke scripts/kconfig/merge_config.sh directly in buildman, or replace our current rule that uses $(CPP) (and has issues with clang) and invoke merge_config.sh in such a way that buildman will then learn what it needs to learn from the resulting config file.