greybus: firmware: Don't send control-disconnected event for firmware protocol

After downloading the firmware for the next boot stage, module's
firmware (for current boot stage) jumps into it and the new firmware and
sends hotplug request to SVC. On hotplug request from the SVC, the AP
first removes the existing interface.

At this time, there is no point sending disconnected event for the
firmware protocol, for the firmware used in previous stage, as the new
firmware wouldn't be aware about it.

Set flags for firmware protocol to skip control-disconnected operations.

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