media: add SPDX header to media uAPI files

All those files are under GFDL 1.1 or later, with no invariant sections.
Tag them as such.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/v4l/subdev-image-processing-scaling-multi-source.svg

@@ -1,4 +1,14 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!--
+    Permission is granted to copy, distribute and/or modify this
+    document under the terms of the GNU Free Documentation License,
+    Version 1.1 or any later version published by the Free Software
+    Foundation, with no Invariant Sections, no Front-Cover Texts
+    and no Back-Cover Texts. A copy of the license is included at
+    Documentation/media/uapi/fdl-appendix.rst.
+
+    TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+-->
 <svg
    xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:cc="http://creativecommons.org/ns#"