feat(trbe): enable access to trace buffer control registers from lower NS EL

Introduced a build flag 'ENABLE_TRBE_FOR_NS' to enable trace buffer
control registers access in NS-EL2, or NS-EL1 (when NS-EL2 is
implemented but unused).

Change-Id: I285a672ccd395eebd377714c992bb21062a729cc
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/include/lib/extensions/trbe.h b/include/lib/extensions/trbe.h
new file mode 100644
index 0000000..1753ab6
--- /dev/null
+++ b/include/lib/extensions/trbe.h
@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2021, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef TRBE_H
+#define TRBE_H
+
+void trbe_enable(void);
+
+#endif /* TRBE_H */