rockchip: dts: rk3399-puma: make the DTS dual-licensed

The RK3399-Q7 (Puma) DTS should (of course) be dual-licensed.
This updates the licensing info in the rk3399-puma.dts.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>