Extract updated kernel configuration after olddefconfig

[emkll]

Currently the script will run make olddefconfig on the appropriate kernel config provided in the configs folder. Because we would like to commit to version control the exact config that is shipping in built kernels, we can add a step during the build process to copy the config of the build kernel into the configs folder to allow a developer to easily commit the config to version control after the kernel was built (and avoid the manual step to fetching the configuration, either by booting into the kernel or inspecting the source tarball produced by the build)