[media] cx88: move width, height and field to core struct

The width, height and field values are core fields since both vbi, video
and blackbird use the same video input.

Move those fields to the correct struct.

Also fix the field checks in the try_fmt functions: add V4L2_FIELD_SEQ_BT/TB
support and map incorrect field values to a correct field value instead of
returning an error.

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