greybus: svc: support status in svc_intf_activate response

Update per Greybus spec. Status attribute added to activate
response to return more detailed information about errors during
activate. If the Greybus response is GB_OP_SUCCESS, the caller
must also check the status attribute in the response to determine
if any other errors occurred.

Testing done: along with matchine firmware change, verified that modules
              were detected and enumerated as expected.

Signed-off-by: Jeffrey Carlyle <jcarlyle@google.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>