greybus: interface: fix timesync registration sequencing

When enabling an interface, control device should be registered after
having successfully added the timesync. Similarly for the interface
disable path, control device should be removed first before removing
timesync.

Testing Done:
 - Enable and disable the interface

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