ARM: dts: tx28: restructure and update DTS file

Update the Ka-Ro TX28 DTS file.

- add Copyright header
- use label references for better readability
- sort the entries alphabetically
- add some aliases used by U-Boot to modify the DT data
Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>