dm: fix DM_EVENT dependencies

CONFIG_DM_EVENT without CONFIG_EVENT is non-functional.
Let CONFIG_DM_EVENT depend on CONFIG_EVENT.

Remove superfluous stub in include/event.h.

Fixes: 5b896ed5856f ("event: Add events for device probe/remove")
Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/event.h b/include/event.h
index 62e72a7..7765f07 100644
--- a/include/event.h
+++ b/include/event.h
@@ -144,7 +144,6 @@
 /** event_show_spy_list( - Show a list of event spies */
 void event_show_spy_list(void);
 
-#if CONFIG_IS_ENABLED(EVENT)
 /**
  * event_notify() - notify spies about an event
  *
@@ -159,6 +158,7 @@
  */
 int event_notify(enum event_t type, void *data, int size);
 
+#if CONFIG_IS_ENABLED(EVENT)
 /**
  * event_notify_null() - notify spies about an event
  *
@@ -169,11 +169,6 @@
  */
 int event_notify_null(enum event_t type);
 #else
-static inline int event_notify(enum event_t type, void *data, int size)
-{
-	return 0;
-}
-
 static inline int event_notify_null(enum event_t type)
 {
 	return 0;