kern-tools: Add SPDX license headers to source files

kern-tools: Add SPDX license headers to source files

Integrating the following commit:

    Add SPDX license headers to source files

    Kconfiglib/* were under ISC license before they were imported
    here from https://github.com/ulfalizer/Kconfiglib
    Adjusting SPDX header to reflect that fact.

    tools/* all have some sort of GPLv2 headers; adding SPDX header
    to make it obvious.

    This address bug #13334 :
    https://bugzilla.yoctoproject.org/show_bug.cgi?id=13334

    Change-Id: I243f2dd266a398f982798b771e74a67be70ecb52
    Signed-off-by: William Bourque <wbourque@gmail.com>
(From OE-Core rev: eb60f1544fcafcfed7baecceec4549c4e86989a3)

Signed-off-by: William Bourque <wbourque@gmail.com>
Signen-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>