Remove the static list of media links that were formed at probe time.
These links can instead be created after all registered async subdevices
have been bound in imx_media_probe_complete().

The media links between subdevices that exist in the device tree, can
be created post-async completion by using v4l2_fwnode_parse_link() for
each endpoint node of that subdevice. Note this approach assumes
device-tree ports are equivalent to media pads (pad index equals
port id), and that device-tree endpoints are equivalent to media
links between pads.

Because links are no longer parsed by imx_media_of_parse(), its sole
function is now only to add subdevices that it encounters by walking
the OF graph to the async list, so the function has been renamed
imx_media_add_of_subdevs().

Similarly, the media links between the IPU-internal subdevice pads (the
CSI source pads, and all pads between the vdic, ic-prp, ic-prpenc, and
ic-prpvf subdevices), can be created post-async completion by looping
through the subdevice's media pads and using the const internal_subdev
table.

Because links are no longer parsed by imx_media_add_internal_subdevs(),
this function no longer needs an array of CSI subdevs to form links
from.

In summary, the following functions, which were used to form a list
of media links at probe time, are removed:

imx_media_add_pad_link()
add_internal_links()
of_add_pad_link()

replaced by these functions, called at probe time, which only populate
the async subdev list:

imx_media_add_of_subdevs()
imx_media_add_internal_subdevs()

and these functions, called at async completion, which create the
media links:

imx_media_create_of_links()
imx_media_create_csi_of_links()
imx_media_create_internal_links()
Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>