V4L/DVB (7083): saa7134: enable radio and external analog audio-in on the md2819

It also enumerates now the separate composite input at first
and adds mute ability to radio and external audio-in.

Many thanks to Daftcho Tabakov for reporting the flaws and testing.

Signed-off-by: Hermann Pitton <hermann-pitton@arcor.de>
Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>