[media] dvb_frontend: estimate bandwidth also for DVB-S/S2/Turbo

The needed bandwidth can be estimated using the symbol rate and
the rolloff factor. This could be useful for the frontend drivers,
as they don't need to calculate it themselves.

Reported-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>