add sanity check if linux kernel .config is set and exists
tree22364c053d44d7394bb05f3fcf548c563bfa906a
-rw-r--r-- 1816 .defconfig
-rw-r--r-- 142 .gitignore
-rw-r--r-- 6134 Config.in
-rw-r--r-- 14558 Makefile
-rw-r--r-- 432 TODO
drwxr-xr-x - docs
drwxr-xr-x - package
drwxr-xr-x - project
drwxr-xr-x - target
drwxr-xr-x - toolchain