event: Convert arch_cpu_init_dm() to use events

Instead of a special function, send an event after driver model is inited
and adjust the boards which use this function.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/event.c b/common/event.c
index 4270809..9d67a06 100644
--- a/common/event.c
+++ b/common/event.c
@@ -26,6 +26,7 @@
 	"test",
 
 	/* Events related to driver model */
+	"dm_post_init",
 	"dm_pre_probe",
 	"dm_post_probe",
 	"dm_pre_remove",