V4L/DVB (10249): v4l2-common: added v4l2_i2c_tuner_addrs()

Add v4l2_i2c_tuner_addrs() to obtain the various I2C tuner addresses.
This will be used in several drivers, so make this a common function
as we do not want to have these I2C addresses all over the place.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>