greybus: connection: drop the legacy protocol-id parameter

The protocol-id parameter is only used by the legacy driver so remove
it from the generic interface and move it to the legacy driver until it
can be removed completely.

Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>