venus: properly expose KHR_external_fence/sempahore_fd
What does this MR do and why?
venus: properly expose KHR_external_fence/sempahore_fd
Summary:
- hide those extensions for vtest since there's no export support
- do block waiting upon export without implicit fencing support
Fixes: 68a47887 ("venus: expose KHR_external_fence/sempahore_fd extensions")
/cc @igor.torrente
Edited by Yiwei Zhang