[media] DiB8000: add diversity support

This patch adds a set a functions which allow the handling of multiple
demodulator in a diversity reception chain.

Signed-off-by: Olivier Grenie <olivier.grenie@dibcom.fr>
Signed-off-by: Patrick Boettcher <patrick.boettcher@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>