linux-firmware: correct license for ar3k firmware

linux-firmware: correct license for ar3k firmware

According to the WHENCE file, some a3k firmware files are licensed
under the special ar3k license, while others are licensed under the more
generic Atheros license. Document this by adding extending the
LICENSE_${PN}-ar3k and depending on both of them.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
(cherry picked from commit 8e651814af706285d64b532095fcd6f5f02629ba)
Signed-off-by: Steve Sakoman <steve@sakoman.com>