[media] af9033: implement DVBv5 post-Viterbi BER

Implement following DTV API commands:
DTV_STAT_POST_ERROR_BIT_COUNT
DTV_STAT_POST_TOTAL_BIT_COUNT

These will provide post-Viterbi bit error rate reporting.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>