greybus: connection: simplify connection-creation interface

Simplify the exported generic interface for creating dynamic
connections.

Since all driver connections will have a bundle we can drop the
redundant interface parameter.

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>