protocol: Provide abstraction over event notification

How this works will be transport-dependent. Move the event notification
helpers into the protocol abstraction and call-back through the
registered flush handler as necessary.

Change-Id: I29e3a9a9785b92de46a2b2750257fb7f8480a184
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/test/bmc_event_ack_v2.c b/test/bmc_event_ack_v2.c
index 3bf1f37..c9056de 100644
--- a/test/bmc_event_ack_v2.c
+++ b/test/bmc_event_ack_v2.c
@@ -49,7 +49,7 @@
 	rc = mbox_command_dispatch(ctx, get_info, sizeof(get_info));
 	assert(rc == 1);
 
-	set_bmc_events(ctx, FLAGS, SET_BMC_EVENT);
+	protocol_events_set(ctx, FLAGS, EVENT_TRIGGER);
 
 	rc = mbox_command_dispatch(ctx, command, sizeof(command));
 	assert(rc == 1);