greybus: hd: fix svc-connection handling

Create the svc connection when registering the host-device and
remove the current svc connection hacks that "upgraded" the svc
connection once the endo id and ap interface id was known.

Note that the old implementation was partly based on a misunderstanding
as it was the remote interface id, rather than the local AP interface id,
that used to define a connection (but we also needed the endo_id).

The remote interface is no longer needed as static connections, such as
the svc connection, are now simply defined by the host-device and host
cport id.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>