V4L/DVB (10499): saa7146: convert saa7146 and mxb in particular to v4l2_subdev.

Modified mxb to load the i2c modules through v4l2_subdev. So no more probing.
Modified tea6415c and tea6420 to use the standard routing ops to do the
routing, rather than using private commands. Dropped the private commands
from tda9840 (they were never used except during initialization of the
module).

Added saa7146 support for VIDIOC_DBG_G_CHIP_IDENT.

Converted saa5246a and saa5249 to v4l2_subdev.

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