libcamera: Add missing SPDX headers

Multiple files in libcamera are missing SPDX headers. Add them with the
following licenses:

- CC-BY-SA-4.0 for documentation

- CC0-1.0 for build system, development tool configuration files and
  TODO lists, as we consider them non-copyrightable, and for example
  configuration files to facilitate their use

- BSD-2-Clause for a file copied from the Raspberry Pi tuning tool (and
  add the corresponding copyright information)

While at it, add a missing blank line to
src/libcamera/pipeline/virtual/README.md.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>

utils/tuning/config-example.yaml

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: CC0-1.0
 general:
   disable: []
   plot: []

utils/tuning/libtuning/ctt_colors.py

@@ -1,4 +1,9 @@
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (C) 2023, Raspberry Pi Ltd
+#
 # Program to convert from RGB to LAB color space
+
 def RGB_to_LAB(RGB):  # where RGB is a 1x3 array.   e.g RGB = [100, 255, 230]
     num = 0
     XYZ = [0, 0, 0]

utils/tuning/requirements.txt

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: CC0-1.0
 coloredlogs
 matplotlib
 numpy