[media] DocBook: Add entry IDs for the enums defined at dvbproperty.xml

There are lots of enums that are defined at dvbproperty.

Add xrefs for each entry there. This makes the hyperlinks at
frontend.h to go directly to the right documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>