[AArch64] make +dit non-FMV-only (#90987)

Required to fix an llvm-test-suite failure:

    error: expected writable system register or pstate: "msr DIT, x0"

Author: tmatheson-arm

llvm/lib/Target/AArch64/AArch64Features.td

@@ -71,7 +71,6 @@ class FMVOnlyExtension<string FMVBit, string Name, string Deps, int Priority>
 }
 
 def : FMVOnlyExtension<"FEAT_DGH", "dgh", "", 260>;
-def : FMVOnlyExtension<"FEAT_DIT", "dit", "+dit", 180>;
 def : FMVOnlyExtension<"FEAT_DPB", "dpb", "+ccpp", 190>;
 def : FMVOnlyExtension<"FEAT_DPB2", "dpb2", "+ccpp,+ccdp", 200>;
 def : FMVOnlyExtension<"FEAT_EBF16", "ebf16", "+bf16", 290>;
@@ -455,9 +454,10 @@ def FeatureMPAM : SubtargetFeature<
     "mpam", "HasMPAM", "true",
     "Enable v8.4-A Memory system Partitioning and Monitoring extension (FEAT_MPAM)">;
 
-def FeatureDIT : SubtargetFeature<
-    "dit", "HasDIT", "true",
-    "Enable v8.4-A Data Independent Timing instructions (FEAT_DIT)">;
+def FeatureDIT : Extension<
+    "dit", "DIT",
+    "Enable v8.4-A Data Independent Timing instructions (FEAT_DIT)", [],
+    "FEAT_DIT", "+dit", 180>;
 
 def FeatureTRACEV8_4 : SubtargetFeature<
     "tracev8.4", "HasTRACEV8_4", "true",