[media] dvb: Add DVBv5 statistics properties

The DVBv3 statistics parameters are limited on several ways:
        - It doesn't provide any way to indicate the used measure,
	  so userspace need to guess how to calculate/use it;
        - Only a limited set of stats are supported;
        - Can't be called in a way to require them to be filled
          all at once (atomic reads from the hardware), with may
          cause troubles on interpreting them on userspace;
        - On some OFDM delivery systems, the carriers can be
          independently modulated, having different properties.
          Currently, there's no way to report per-layer stats.
To address the above issues, adding a new DVBv5-based stats API.
While here, correct inner code nomenclature on a few places.

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