arm: socfpga: dts: Move to SPDX license identifiers

arm: socfpga: dts: Move to SPDX license identifiers

The socfpga dts files are copied from the Rocketboards.org repository.
In U-Boot we usually replace the full-blown license header text with
the SPDX license identifiers. Lets do this for these new dts files
as well.

I just forgot to do this while adding the DT support for socfpga.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Marek Vasut <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Vince Bridgers <[email protected]>