SDEI: Add API for explicit dispatch

This allows for other EL3 components to schedule an SDEI event dispatch
to Normal world upon the next ERET. The API usage constrains are set out
in the SDEI dispatcher documentation.

Documentation to follow.

Change-Id: Id534bae0fd85afc94523490098c81f85c4e8f019
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/include/services/sdei.h b/include/services/sdei.h
index 72eb6d7..b07e93b 100644
--- a/include/services/sdei.h
+++ b/include/services/sdei.h
@@ -175,4 +175,7 @@
 
 void sdei_init(void);
 
+/* Public API to dispatch an event to Normal world */
+int sdei_dispatch_event(int ev_num, unsigned int preempted_sec_state);
+
 #endif /* __SDEI_H__ */