Update all 32bit rockchip devicetree files to use SPDX-License-Identifiers.

All files except rk3288-veyron-analog-audio.dtsi (which is GPL 2.0 only)
claim to be GPL and X11 while the actual license text is MIT. Use the
MIT SPDX tag for them.
Signed-off-by: NKlaus Goger <klaus.goger@theobroma-systems.com>
Acked-by: NBrian Norris <briannorris@chromium.org>
Acked-by: NMatthias Brugger <mbrugger@suse.com>
Acked-by: NDouglas Anderson <dianders@chromium.org>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>