ARM: sun7i: cubieboard2: Relicense the device tree under GPLv2/X11

The current GPL only licensing on the DTSI makes it very impractical for other
software components licensed under another license.

In order to make it easier for them to reuse our device trees, relicense our
device trees under a GPL/X11 dual-license.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Alexander Bersenev <bay@hackerdom.ru>
Acked-by: Carlo Caione <carlo@caione.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Roman Byshko <rbyshko@gmail.com>