refactor(plat/ffa): refactor notifications

* Introduce `ffa_notifications_flags_t` typedef
* Document notification flag related macros
* Return a `struct ffa_value` from
  `plat_ffa_notifications_get_framework_notifications` instead of
  mutating an out parameter.
* Remove unused function declarations

Change-Id: Ia56acdccbe9f23a0ee1b541a10c56bad6ea40fca
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/inc/hf/api.h b/inc/hf/api.h
index bc5bedf..a7108f5 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -129,16 +129,19 @@
 						     struct vcpu *current);
 
 struct ffa_value api_ffa_notification_update_bindings(
-	ffa_id_t sender_vm_id, ffa_id_t receiver_vm_id, uint32_t flags,
+	ffa_id_t sender_vm_id, ffa_id_t receiver_vm_id,
+	ffa_notification_flags_t flags,
 	ffa_notifications_bitmap_t notifications, bool is_bind,
 	struct vcpu *current);
 
 struct ffa_value api_ffa_notification_set(
-	ffa_id_t sender_vm_id, ffa_id_t receiver_vm_id, uint32_t flags,
+	ffa_id_t sender_vm_id, ffa_id_t receiver_vm_id,
+	ffa_notification_flags_t flags,
 	ffa_notifications_bitmap_t notifications, struct vcpu *current);
 
 struct ffa_value api_ffa_notification_get(ffa_id_t receiver_vm_id,
-					  uint16_t vcpu_id, uint32_t flags,
+					  uint16_t vcpu_id,
+					  ffa_notification_flags_t flags,
 					  struct vcpu *current);
 
 struct ffa_value api_ffa_notification_info_get(struct vcpu *current);