refactor(amu): unify ENABLE_AMU and ENABLE_FEAT_AMUv1

So far we have the ENABLE_AMU build option to include AMU register
handling code for enabling and context switch. There is also an
ENABLE_FEAT_AMUv1 option, solely to protect the HAFGRTR_EL2 system
register handling. The latter needs some alignment with the new feature
scheme, but it conceptually overlaps with the ENABLE_AMU option.

Since there is no real need for two separate options, unify both into a
new ENABLE_FEAT_AMU name in a first step. This is mostly just renaming at
this point, a subsequent patch will make use of the new feature handling
scheme.

Change-Id: I97d8a55bdee2ed1e1509fa9f2b09fd0bdd82736e
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index d3c6263..f827895 100644
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -244,11 +244,11 @@
 
 static inline bool is_feat_amu_supported(void)
 {
-	if (ENABLE_FEAT_AMUv1 == FEAT_STATE_DISABLED) {
+	if (ENABLE_FEAT_AMU == FEAT_STATE_DISABLED) {
 		return false;
 	}
 
-	if (ENABLE_FEAT_AMUv1 == FEAT_STATE_ALWAYS) {
+	if (ENABLE_FEAT_AMU == FEAT_STATE_ALWAYS) {
 		return true;
 	}