conf.py: Improve TOC and Outline depth in PDF output

The default PDF output shows only chapter headings in the table of
contents and in the outline (aka PDF bookmarks). We should override
these defaults to set something more suitable.

With a depth of 2 for the TOC we see both section and subsection
headings which is enough to get the list of classes in the reference
manual and the list of topics under "Common Tasks" in the development
manual. Going to a deeper level would make the TOC unwieldy but we do
want to make sure we can navigate more precisely using the outline
(commonly shown in a left tab in PDF viewers) so we set the depth to 5
for the outline.

(From yocto-docs rev: 5db16d3b01da0a138b6413347fcf2321a1bfae08)

Signed-off-by: Paul Barker <pbarker@konsulko.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/conf.py

@@ -124,3 +124,8 @@ html_last_updated_fmt = '%b %d, %Y'
 
 # Remove the trailing 'dot' in section numbers
 html_secnumber_suffix = " "
+
+latex_elements = {
+    'passoptionstopackages': '\PassOptionsToPackage{bookmarksdepth=5}{hyperref}',
+    'preamble': '\setcounter{tocdepth}{2}',
+}