fix(build): correct feature assignment for ARM v8.8 compliance

Correct feature list assignment to apply ARM v8.7 features
to `armv8-8-a-feats` instead of `armv8-7-a-feats` for ARM v8.8
compliance.
This was highlighted during the build of TC4 with ARM_ARCH_MAJOR=8
and ARM_ARCH_MINOR=8.

Change-Id: I6c48a3ffa2f1e18d5e4a6484a823c9112dddd751
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/make_helpers/arch_features.mk b/make_helpers/arch_features.mk
index d378a55..57609d5 100644
--- a/make_helpers/arch_features.mk
+++ b/make_helpers/arch_features.mk
@@ -84,7 +84,7 @@
 # Enable the features which are mandatory from ARCH version 8.8 and upwards.
 ifeq "8.8" "$(word 1, $(sort 8.8 $(ARM_ARCH_MAJOR).$(ARM_ARCH_MINOR)))"
 # 8.7 Compliant
-armv8-7-a-feats         += ${armv8-7-a-feats}
+armv8-8-a-feats         += ${armv8-7-a-feats}
 FEAT_LIST               := ${armv8-8-a-feats}
 endif