LICENSES: add dual/CC-BY-4.0

LICENSES: add dual/CC-BY-4.0

The license CC-BY-4.0 is not compatible with GPLv2, but files can
be dual licensed with a GPLv2 compatible license 'OR' CC-BY-4.0.

This is the case for some file auto-generated by riscv project.

Change-Id: I4313d85a569a5e6423392129a730d1e22ef17c51
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8894
Reviewed-by: Bernhard Rosenkraenzer <bero@baylibre.com>
Tested-by: jenkins