chore(npcm845x): remove pauth_helpers.S additions in platform makefile

Currently 'pauth_helpers.S' is added if pauth is enabled from main
level makefile.

Change-Id: I33800e280daea6dba6d11e2c494101b369cd8a0b
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/plat/nuvoton/npcm845x/platform.mk b/plat/nuvoton/npcm845x/platform.mk
index 7fbf11e..5120cc6 100644
--- a/plat/nuvoton/npcm845x/platform.mk
+++ b/plat/nuvoton/npcm845x/platform.mk
@@ -299,8 +299,7 @@
 
 # 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)