media: v4l2-fwnode: add initial connector parsing support

The patch adds the initial connector parsing code, so we can move from a
driver specific parsing code to a generic one. Currently only the
generic fields and the analog-connector specific fields are parsed. Parsing
the other connector specific fields can be added by a simple callbacks.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
[hverkuil-cisco@xs4all.nl: replace ; with break; in a empty case]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>