Fix crash dump for lower EL

This patch provides a fix for incorrect crash dump data for
lower EL when TF-A is built with HANDLE_EA_EL3_FIRST=1 option
which enables routing of External Aborts and SErrors to EL3.

Change-Id: I9d5e6775e6aad21db5b78362da6c3a3d897df977
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
diff --git a/include/common/debug.h b/include/common/debug.h
index 245e698..9aef15b 100644
--- a/include/common/debug.h
+++ b/include/common/debug.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -91,6 +91,7 @@
 
 #if ENABLE_BACKTRACE
 void backtrace(const char *cookie);
+const char *get_el_str(unsigned int el);
 #else
 #define backtrace(x)
 #endif