[media] tm6000: Improve audio standards handling and add SECAM-DK

Rework audio. Add SECAM-DK, move SECAM to SECAM-B | SECAM-G.

Add some new audio standards and tricks for future, see
tm6000_set_audio_std.

For SECAM-DK it works.
Signed-off-by: Beholder Intl. Ltd. Dmitry Belimov <d.belimov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>