V4L/DVB (8523): v4l2-dev: remove unused type and type2 field from video_device

The type and type2 fields were unused and so could be removed.
Instead add a vfl_type field that contains the type of the video
device.

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