NIL documentation build works.

git-svn-id: http://svn.code.sf.net/p/chibios/svn/trunk@7565 35acf78f-673a-0410-8e92-d51de3d6d3f4
git-svn-id: http://svn.code.sf.net/p/chibios/svn/trunk@7566 35acf78f-673a-0410-8e92-d51de3d6d3f4