V4L/DVB (13247): tuner-core: dont force every tuner to set frequency at startup

Setting the tuner frequency at the same time as initializing the other devices
on the i2c bus can cause problems on devices that require firmware download or
extensive calibration proceduces during initialization.

This change allows us to prevent the tune at startup for devices that perform
better without it.

Signed-off-by: Michael Krufky <mkrufky@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>