Build kernel images from source tarball

[emkll]

The project meant to be replaced by this kernel-builder project provides the user with the ability to rebuild a kernel image from a source tarball: https://github.com/freedomofpress/ansible-role-grsecurity-build/blob/2f01f43697992c7353db3083e5689493c36ea4e5/Makefile#L4 .In order to provide feature parity with that repository, we should add the option to rebuild a kernel from a local tarball (without fetching patches or any configuration changes, simply building a kernel from the tarball).