V4L/DVB (8941): mxb/tda9840: cleanups, use module saa7115 instead of saa7111.

Cleanup tda9840 and use a v4l2 API to get the tuner subchannels.
Do some cleanups in mxb and switch to saa7115 instead of the saa7111
module.

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