[media] davinci: vpif_capture: cleanup raw camera support

The current driver has a handful of hard-coded assumptions based on its
primary use for capture of video signals.  Cleanup those assumptions,
and also query the subdev for format information and use that if
available.

Tested with 10-bit raw bayer input (SGRBG10) using the aptina,mt9v032
sensor, and also tested that composite video input still works from
ti,tvp514x decoder.  Both tests done on the da850-evm board with the
add-on UI board.

NOTE: Will need further testing for other sensors with different bus
formats.

Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>