[media] tea575x-tuner: move HW init to a separate function

Move HW initialization to separate function to allow using the code without
the v4l parts. This is needed for use in the bttv driver.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>