[AArch64] Fix list of features for Cortex-X1C

This patch fixes the list of subtarget features enabled for the
Cortex-X1C processor, including the following:

* Fix incorrect version used for FeatureRCPC:
  * Use FEAT_LRCPC2 instead of FEAT_LRCPC.
* Add missing v8.4-A features included in the TRM:
  * Flag Manipulation Instructions - FeatureFlagM (FEAT_FlagM)
  * Large System Extension 2 - FeatureLSE2 (FEAT_LSE2)

Reviewed By: vhscampos

Differential Revision: https://reviews.llvm.org/D132120

llvm/lib/Target/AArch64/AArch64.td

@@ -1033,9 +1033,10 @@ def ProcessorFeatures {
                                  FeatureSPE, FeatureFullFP16, FeatureDotProd,
                                  FeatureSSBS];
   list<SubtargetFeature> X1C  = [HasV8_2aOps, FeatureCrypto, FeatureFPARMv8,
-                                 FeatureNEON, FeatureRCPC, FeaturePerfMon,
+                                 FeatureNEON, FeatureRCPC_IMMO, FeaturePerfMon,
                                  FeatureSPE, FeatureFullFP16, FeatureDotProd,
-                                 FeaturePAuth, FeatureSSBS];
+                                 FeaturePAuth, FeatureSSBS, FeatureFlagM,
+                                 FeatureLSE2];
   list<SubtargetFeature> X2   = [HasV9_0aOps, FeatureNEON, FeaturePerfMon,
                                  FeatureMatMulInt8, FeatureBF16, FeatureAM,
                                  FeatureMTE, FeatureETE, FeatureSVE2BitPerm,