feat(rng-trap): add EL3 support for FEAT_RNG_TRAP

FEAT_RNG_TRAP introduces support for EL3 trapping of reads of the
RNDR and RNDRRS registers, which is enabled by setting the
SCR_EL3.TRNDR bit. This patch adds a new build flag
ENABLE_FEAT_RNG_TRAP that enables the feature.
This feature is supported only in AArch64 state from Armv8.5 onwards.

Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
Change-Id: Ia9f17aef3444d3822bf03809036a1f668c9f2d89
diff --git a/Makefile b/Makefile
index ee5e2e7..8d8facd 100644
--- a/Makefile
+++ b/Makefile
@@ -788,11 +788,15 @@
         $(error "ENABLE_SVE_FOR_NS cannot be used with ARCH=aarch32")
     endif
 
-    # BRBE is not supported in Aarch32
+    # BRBE is not supported in AArch32
     ifeq (${ENABLE_BRBE_FOR_NS},1)
         $(error "ENABLE_BRBE_FOR_NS cannot be used with ARCH=aarch32")
     endif
 
+    # FEAT_RNG_TRAP is not supported in AArch32
+    ifeq (${ENABLE_FEAT_RNG_TRAP},1)
+        $(error "ENABLE_FEAT_RNG_TRAP cannot be used with ARCH=aarch32")
+    endif
 endif
 
 # Ensure ENABLE_RME is not used with SME
@@ -1073,6 +1077,7 @@
         ENABLE_FEAT_HCX \
         ENABLE_FEAT_PAN \
         ENABLE_FEAT_RNG \
+        ENABLE_FEAT_RNG_TRAP \
         ENABLE_FEAT_SB \
         ENABLE_FEAT_SEL2 \
         ENABLE_FEAT_VHE \
@@ -1183,6 +1188,7 @@
         COT_DESC_IN_DTB \
         USE_SP804_TIMER \
         ENABLE_FEAT_RNG \
+        ENABLE_FEAT_RNG_TRAP \
         ENABLE_FEAT_SB \
         ENABLE_FEAT_DIT \
         NR_OF_FW_BANKS \