context_mgmt: Fix MISRA defects

The macro EL_IMPLEMENTED() has been deprecated in favour of the new
function el_implemented().

Change-Id: Ic9b1b81480b5e019b50a050e8c1a199991bf0ca9
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/lib/el3_runtime/context_mgmt.h b/include/lib/el3_runtime/context_mgmt.h
index c5bbb2b..149ac3f 100644
--- a/include/lib/el3_runtime/context_mgmt.h
+++ b/include/lib/el3_runtime/context_mgmt.h
@@ -1,16 +1,15 @@
 /*
- * Copyright (c) 2013-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __CM_H__
-#define __CM_H__
+#ifndef CONTEXT_MGMT_H
+#define CONTEXT_MGMT_H
 
 #include <arch.h>
 #include <assert.h>
 #include <context.h>
-#include <context_mgmt.h>
 #include <stdint.h>
 
 /*******************************************************************************
@@ -80,4 +79,4 @@
 void cm_set_next_context(void *context);
 #endif /* AARCH32 */
 
-#endif /* __CM_H__ */
+#endif /* CONTEXT_MGMT_H */