bloblist: Relicense to allow BSD-3-Clause

This implementation is intended to be copied to other projects and
modified, to as to foster a standard means of communcating runtime
information between firmware projects.

The GPL-2 license is too restrictive for some projects, e.g. those
intended as reference implementations rather than designed for
collaborative open-source development.

Update the license to make this easier to share.

Signed-off-by: Simon Glass <sjg@chromium.org>