pylibfdt: correct license information (further)

Since commit 51ec8db232 ("pylibfdt: correct license information"), the
License classifiers are gone so I assume setuptools now extract the
license from the license argument to setuptools.setup() function.

It's always been incorrect as far as I could tell, so let's fix this
with the appropriate info from the SPDX License identifier at the top of
the file. It was missing GPL-2.0-or-later and we disambiguate by using
BSD-2-Clause instead of simply BSD.

Fixes: 6b08fb5cc4 ("fdt: Move to setuptools")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>

scripts/dtc/pylibfdt/setup.py

@@ -157,7 +157,7 @@ setup(
     long_description=long_description,
     long_description_content_type="text/plain",
     url="https://git.kernel.org/pub/scm/utils/dtc/dtc.git",
-    license="BSD",
+    license="GPL-2.0-or-later OR BSD-2-Clause",
     license_files=["Licenses/gpl-2.0.txt", "Licenses/bsd-2-clause.txt"],
 
     classifiers=[