greybus: connection: add no-flow-control connection flag

Add a no-flow-control connection flag, which is set for connection that
should not have any flow-control feature enabled.

This flag is specifically set for all connections to the legacy ES3
bootrom, and will also be used by the camera driver eventually.

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