fix(pauth): make pauth_helpers linking generic

Pauth is a generic Arm feature that can be enabled on any platform that
implements it. It only needs a platform specific key generation hook. As
such, the generic Pauth enablement can be included in the generic build.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ibf32f79addab3515214594bb8d7168151b450f59
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 7162ce9..4fabdfc 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -353,8 +353,7 @@
 
 # Pointer Authentication sources
 ifeq (${ENABLE_PAUTH}, 1)
-PLAT_BL_COMMON_SOURCES	+=	plat/arm/common/aarch64/arm_pauth.c	\
-				lib/extensions/pauth/pauth_helpers.S
+PLAT_BL_COMMON_SOURCES	+=	plat/arm/common/aarch64/arm_pauth.c
 endif
 
 ifeq (${SPD},spmd)