media: v4l: fwnode: Let the caller provide V4L2 fwnode endpoint

Instead of allocating the V4L2 fwnode endpoint in
v4l2_fwnode_endpoint_alloc_parse, let the caller to do this. This allows
setting default parameters for the endpoint which is a very common need
for drivers.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>