fconf: Add TBBR disable_authentication property

Use fconf to retrieve the `disable_authentication` property.
Move this access from arm dynamic configuration to bl common.

Change-Id: Ibf184a5c6245d04839222f5457cf5e651f252b86
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
diff --git a/common/bl_common.c b/common/bl_common.c
index b74225b..2fcb538 100644
--- a/common/bl_common.c
+++ b/common/bl_common.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */