V4L/DVB (8021): Beholder's cards description

Split the Beholder M6 family to different models. Because M6 hasn`t RDS, M63
has chip with AC3 codec, M6 Extra has other type of HF module.
Add correct data for support MPEG encoder.

Signed-off-by: Beholder Intl. Ltd. Dmitry Belimov <d.belimov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>