arm64: dts: rockchip: use SPDX-License-Identifier

Update all 64bit rockchip devicetree files to use SPDX-License-Identifiers.

All devicetrees claim to be either GPL or X11 while the actual license
text is MIT. Therefore we use MIT for the SPDX tag as X11 is clearly
wrong.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Acked-by: Brian Norris <briannorris@chromium.org>
Acked-by: Matthias Brugger <mbrugger@suse.com>
Acked-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>