V4L/DVB (13160): DocBook/Makefile: add linux/dvb/frontend.h header file

Adds linux/dvb/frontend.h header file at DocBook, and creates cross-references
for the frontend ioctls.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/dvb/dvbapi.xml b/Documentation/DocBook/dvb/dvbapi.xml
index 4fc5b23..a007f88 100644
--- a/Documentation/DocBook/dvb/dvbapi.xml
+++ b/Documentation/DocBook/dvb/dvbapi.xml
@@ -85,3 +85,8 @@
     &sub-examples;
   </chapter>
 <!-- END OF CHAPTERS -->
+  <appendix id="frontend_h">
+    <title>DVB Frontend Header File</title>
+    &sub-frontend-h;
+  </appendix>
+