mediatek: fix SPDX license identifier on local DTS files

mediatek: fix SPDX license identifier on local DTS files

The SPDX license identifier must be in the first line of a file,
unless there is a shebang (then it's the second line).

Fix this for the local files, do not care about the upstream patches.

While at it, update the identifiers where necessary.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>