west: spdx: allow to generate for different SPDX versions

When support for SPDX 2.3 was added, it effectively dropped support for
SPDX 2.2, which in retrospect was a bad idea since SPDX 2.2 is the
version that is the current ISO/IEC standard.
This commit adds a `--spdx-version` option to the `west spdx` command
so that users can generate SPDX 2.2 documents if they want.
Default is 2.3 given that's effectively what shipped for a few releases
now, including latest LTS.

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

doc/develop/west/zephyr-cmds.rst

@@ -75,7 +75,7 @@ See :zephyr_file:`share/zephyr-package/cmake` for details.
 Software bill of materials: ``west spdx``
 *****************************************
 
-This command generates SPDX 2.3 tag-value documents, creating relationships
+This command generates SPDX 2.2 or 2.3 tag-value documents, creating relationships
 from source files to the corresponding generated build files.
 ``SPDX-License-Identifier`` comments in source files are scanned and filled
 into the SPDX documents.
@@ -105,6 +105,12 @@ To use this command:
 
       west spdx -d BUILD_DIR
 
+   By default, this generates SPDX 2.3 documents. To generate SPDX 2.2 documents instead:
+
+   .. code-block:: bash
+
+      west spdx -d BUILD_DIR --spdx-version 2.2
+
 .. note::
 
    When building with :ref:`sysbuild`, make sure you target the actual application
@@ -144,6 +150,10 @@ source files that are compiled to generate the built library files.
 - ``-s SPDX_DIR``: specifies an alternate directory where the SPDX documents
   should be written instead of :file:`BUILD_DIR/spdx/`.
 
+- ``--spdx-version {2.2,2.3}``: specifies which SPDX specification version to use.
+  Defaults to ``2.3``. SPDX 2.3 includes additional fields like ``PrimaryPackagePurpose``
+  that are not available in SPDX 2.2.
+
 - ``--analyze-includes``: in addition to recording the compiled source code
   files (e.g. ``.c``, ``.S``) in the bills-of-materials, also attempt to
   determine the specific header files that are included for each ``.c`` file.