Makefile: Add FEAT_RNG support define

Define ENABLE_FEAT_RNG that describes whether the
armv8.5 FEAT_RNG is supported in this build. This
allows conditional inclusion of code targetting
RNDR and RNDRRS registers.
Signed-off-by: Tomas Pilar <tomas@nuviainc.com>
Change-Id: Idd632f8b9bc20ea3d8793f55ead88fa12cb08821

Makefile

@@ -242,6 +242,9 @@ endif
 $(info Arm Architecture Features specified: $(subst +, ,$(arch-features)))
 endif	# arch-features
 
+# Determine if FEAT_RNG is supported
+ENABLE_FEAT_RNG		=	$(if $(findstring rng,${arch-features}),1,0)
+
 ifneq ($(findstring armclang,$(notdir $(CC))),)
 TF_CFLAGS_aarch32	=	-target arm-arm-none-eabi $(march32-directive)
 TF_CFLAGS_aarch64	=	-target aarch64-arm-none-eabi $(march64-directive)
@@ -940,6 +943,7 @@ $(eval $(call assert_booleans,\
         RAS_TRAP_LOWER_EL_ERR_ACCESS \
         COT_DESC_IN_DTB \
         USE_SP804_TIMER \
+        ENABLE_FEAT_RNG \
 )))
 
 $(eval $(call assert_numerics,\
@@ -1030,6 +1034,7 @@ $(eval $(call add_defines,\
         RAS_TRAP_LOWER_EL_ERR_ACCESS \
         COT_DESC_IN_DTB \
         USE_SP804_TIMER \
+        ENABLE_FEAT_RNG \
 )))
 
 ifeq (${SANITIZE_UB},trap)