GPLv2-only devicetrees make reuse difficult for software components licensed
under a different license.

The consensus is that a GPL/X11 dual-license should allow all necessary uses,
so relicense the rk3xxx.dtsi to this combination.

CCs were aquired by git shortlog -sne so it should've hopefully catched
every contributor.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Beniamino Galvani <b.galvani@gmail.com>
Acked-by: Romain Perier <romain.perier@gmail.com>
Acked-by: Julien Chauveau <chauveau.julien@gmail.com>