[ofw][patch][CORE,HW] remove PDO from the upper HCA interface

[Sean Hefty]

>You need open_ca to set async_event_cb.
>But you reminded me someone's (?Fab)idea to allow secondary open_ca's
>with NULL in place of async_event_cb.
>Then there'll be no need in p_hca_obj field.
>I will suggest a patch.

Calls already exist for this.  See ci_register_event_handler_t /
ci_unregister_event_handler_t.  These were added for winverbs.

- Sean