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/media-entities.tmpl b/Documentation/DocBook/media-entities.tmpl
index 0eb43c1..e3f3ad5 100644
--- a/Documentation/DocBook/media-entities.tmpl
+++ b/Documentation/DocBook/media-entities.tmpl
@@ -288,6 +288,7 @@
 <!ENTITY sub-net SYSTEM "dvb/net.xml">
 <!ENTITY sub-kdapi SYSTEM "dvb/kdapi.xml">
 <!ENTITY sub-examples SYSTEM "dvb/examples.xml">
+<!ENTITY sub-frontend-h SYSTEM "dvb/frontend.h.xml">
 <!ENTITY sub-dvbapi SYSTEM "dvb/dvbapi.xml">
 <!ENTITY sub-media SYSTEM "media.xml">
 <!ENTITY sub-media-entities SYSTEM "media-entities.tmpl">