Doc: Remove external libraries from documentation

This patch removes all documentes listed under the
path '/lib/ext' from the Sphynx build TOC and adds
the patch to exclusion list.

Change-Id: I7852b030b946d68b359c31ce4a785920a07f4ff5
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/docs/conf.py.in b/docs/conf.py.in
index 39b2e1c..81e1134 100644
--- a/docs/conf.py.in
+++ b/docs/conf.py.in
@@ -82,7 +82,8 @@
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path .
 exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', 'readme.rst',
-                    'platform/ext/target/cypress/psoc64/security/keys/readme.rst']
+                    'platform/ext/target/cypress/psoc64/security/keys/readme.rst',
+                    'lib/ext/**']
 
 # The name of the Pygments (syntax highlighting) style to use.
 pygments_style = 'sphinx'