media: v4l: async: Drop v4l2_async_nf_parse_fwnode_endpoints()

The v4l2_async_nf_parse_fwnode_endpoints() function, part of
v4l2-fwnode.c, was a helper meant to register one async sub-dev for each
fwnode endpoint of a device.

The function is marked as deprecated in the documentation and is actually
not used anywhere anymore. Drop it and remove the helper function
v4l2_async_nf_fwnode_parse_endpoint() from v4l2-fwnode.c.

This change allows to make the helper function
__v4l2_async_nf_add_connection() visibility private to v4l2-async.c so
that there is no risk drivers can mistakenly use it.

[Sakari Ailus: Small fixups on top.]

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de> # imx6qp
Tested-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> # rcar + adv746x
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Aishwarya Kothari <aishwarya.kothari@toradex.com> # Apalis i.MX6Q with TC358743
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # Renesas RZ/G2L SMARC
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>