[media] v4l2-subdev: remove core.s_config and v4l2_i2c_new_subdev_cfg()

The core.s_config op was meant for legacy drivers that needed to work with old
pre-2.6.26 kernels. This is no longer relevant. Unfortunately, this op was
incorrectly called from several drivers.

Replace those occurences with proper i2c_board_info structs and call
v4l2_i2c_new_subdev_board.

After these changes v4l2_i2c_new_subdev_cfg() was no longer used, so remove
that function as well.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>