[media] mn88473: add DVBv5 statistics support

Implement DVBv5 statistics support for DVB-T, DVB-T2 and DVB-C. All
information was taken from the LinuxTV wiki, where Benjamin Larsson has
documented all registers:
https://www.linuxtv.org/wiki/index.php/Panasonic_MN88472



Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>