feat(trf): enable trace filter control register access from lower NS EL

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

Change-Id: If3f53b8173a5573424b9a405a4bd8c206ffdeb8c
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index 060bc38..c188621 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -371,3 +371,8 @@
 # ELs  i.e. NS-EL2, or NS-EL1 if NS-EL2 implemented but unused if
 # system register trace is implemented.
 ENABLE_SYS_REG_TRACE_FOR_NS	:= 0
+
+# By default, disable trace filter control registers access to NS
+# lower ELs, i.e. NS-EL2, or NS-EL1 if NS-EL2 implemented but unused
+# if FEAT_TRF is implemented.
+ENABLE_TRF_FOR_NS		:= 0