V4L/DVB (11088): au0828: finish videodev/subdev conversion

Per Hans Verkuil <hverkuil@xs4all.nl> instruction, remove the deprecated
attach_inform/detach_inform routines, and convert over the i2c calls to
subdev calls.

Thanks to Hans Verkuil <hverkuil@xs4all.nl> for providing feedback on the
au0828 analog support.

Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>