media: dvb: tag deprecated DVB APIs as such

There are three headers at DVB that should not be used on
future projects: audio.h, osd.h and video.h.

While this is already clear at the docs, make clear also at
the headers that those files should not be used on future
drivers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>