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/aarch64/context.h b/include/lib/el3_runtime/aarch64/context.h
index b990674..8c5f4c6 100644
--- a/include/lib/el3_runtime/aarch64/context.h
+++ b/include/lib/el3_runtime/aarch64/context.h
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __CONTEXT_H__
-#define __CONTEXT_H__
+#ifndef CONTEXT_H
+#define CONTEXT_H
 
 #include <utils_def.h>
 
@@ -347,4 +347,4 @@
 
 #endif /* __ASSEMBLY__ */
 
-#endif /* __CONTEXT_H__ */
+#endif /* CONTEXT_H */