kbuild: Do not package /boot and /lib in make tar-pkg

commit fe04ddf7c2910362f3817c8156e41cbd6c0ee35d upstream.

There were reports of users destroying their Fedora installs by a kernel
tarball that replaces the /lib -> /usr/lib symlink. Let's remove the
toplevel directories from the tarball to prevent this from happening.

Reported-by: Andi Kleen <andi@firstfloor.org>
Suggested-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Michal Marek <mmarek@suse.cz>
[bwh: Fold in commit 3ce9e53e788881da0d5f3912f80e0dd6b501f304 to avoid
 conflicts]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>