greybus: interface: clean up ES3 activation-retry hack

Clean up the ES3 activation retry-hack and isolate it in the interface
code.

This way the retry hack can be reused when we soon start allowing
interfaces to be reactivated after having been powered down.

Reviewed-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Patrick Titiano <ptitiano@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>