V4L/DVB (11128): cx231xx: convert the calls to subdev format

This patch converts cx231xx to the new v4l2 dev/subdev, doing:
 - Conversion of i2c calls to subdev calls;
 - all subdev calls to call_all();
 - Corrected the header file order in cx231xx.h;
 - Added tuner frequency setting.

Signed-off-by: Srinivasa Deevi <srinivasa.deevi@conexant.com>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>