Add 'afb_service_call_sync' function

Add 'afb_service_call_sync' function

This new function allows to call features for the
services synchronously.

Also refactoring how are handled arguments to
calls. The call to 'json_object_put' is now always
done by the binder.

Change-Id: I910517da75b179aeafc824da4ce29bc299711990
Signed-off-by: José Bollo <jose.bollo@iot.bzh>