feat(cpufeat): add support for FEAT_PAUTH_LR

This patch enables FEAT_PAUTH_LR at EL3 on systems that support it when
the new ENABLE_FEAT_PAUTH_LR flag is set.

Currently, PAUTH_LR is only supported by arm clang compiler and not GCC.

Change-Id: I7db1e34b661ed95cad75850b62878ac5d98466ea
Signed-off-by: John Powell <john.powell@arm.com>
diff --git a/make_helpers/arch_features.mk b/make_helpers/arch_features.mk
index 56bfb64..1561a59 100644
--- a/make_helpers/arch_features.mk
+++ b/make_helpers/arch_features.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2022-2024, Arm Limited. All rights reserved.
+# Copyright (c) 2022-2025, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -160,6 +160,11 @@
 # direct setting. Use BRANCH_PROTECTION to enable PAUTH.
 ENABLE_PAUTH			?=	0
 
+# FEAT_PAUTH_LR is an optional architectural feature, so this flag must be set
+# manually in addition to the BRANCH_PROTECTION flag which is used for other
+# branch protection and pointer authentication features.
+ENABLE_FEAT_PAUTH_LR		?=	0
+
 # Include pointer authentication (ARMv8.3-PAuth) registers in cpu context. This
 # must be set to 1 if the platform wants to use this feature in the Secure
 # world. It is not necessary for use in the Non-secure world.