AMU: Implement support for aarch64

The `ENABLE_AMU` build option can be used to enable the
architecturally defined AMU counters.  At present, there is no support
for the auxiliary counter group.

Change-Id: I7ea0c0a00327f463199d1b0a481f01dadb09d312
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>
diff --git a/lib/el3_runtime/aarch64/context_mgmt.c b/lib/el3_runtime/aarch64/context_mgmt.c
index 8f1523f..b892729 100644
--- a/lib/el3_runtime/aarch64/context_mgmt.c
+++ b/lib/el3_runtime/aarch64/context_mgmt.c
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
+#include <amu.h>
 #include <arch.h>
 #include <arch_helpers.h>
 #include <assert.h>
@@ -220,6 +221,10 @@
 #if ENABLE_SPE_FOR_LOWER_ELS
 	spe_enable(el2_unused);
 #endif
+
+#if ENABLE_AMU
+	amu_enable(el2_unused);
+#endif
 #endif
 }