doc-rst: make dev-tools folder buildable stand-alone

Add minimal conf.py and moved dev-tools/tools.rst to dev-tools/index.rst
makes the dev-tools folder buildable stand-alone. To build only this
folder run::

  make SPHINXDIRS=dev-tools htmldocs
  make SPHINXDIRS=dev-tools pdfdocs
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/conf.py

+# -*- coding: utf-8; mode: python -*-
+
+project = "Development tools for the kernel"
+
+tags.add("subproject")
+
+latex_documents = [
+    ('index', 'dev-tools.tex', project,
+     'The kernel development community', 'manual'),
+]

Documentation/dev-tools/tools.rst → Documentation/dev-tools/index.rst

@@ -23,3 +23,11 @@ whole; patches welcome!
    kmemleak
    kmemcheck
    gdb-kernel-debugging
+
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/index.rst

@@ -14,7 +14,7 @@ Contents:
    admin-guide/index
    kernel-documentation
    process/index
-   dev-tools/tools
+   dev-tools/index
    driver-api/index
    media/index
    gpu/index