greybus: interface: move interface-removal helper

Move helper to remove all interfaces of a host-device to the svc code
and call it when removing the svc device as this needs to be coordinated
with flushing the SVC work queue.

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