media: si2165: Add DVBv3 wrapper for ber statistics

Add read_ber function that reads from property cache to support DVBv3.
The implementation is inspired by the cx24120 driver.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>