media: v4l2: taint pads with the signal types for consumer devices

Consumer devices are provided with a wide different range of types
supported by the same driver, allowing different configutations.

In order to make easier to setup media controller links, "taint"
pads with the signal type it carries.

While here, get rid of DEMOD_PAD_VBI_OUT, as the signal it carries
is actually the same as the normal video output.

The difference happens at the video/VBI interface:
	- for VBI, only the hidden lines are streamed;
	- for video, the stream is usually cropped to hide the
	  vbi lines.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>