greybus: connection: move CPort Buffer configuration out of svc helpers

The CPort Buffer configuration in the host-device needs to match the
CPort feature flags set by the SVC, but they need not always be
configured at the same point in time.

This will be used when implementing proper connection tear down.

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>