[AArch64] Fix list of features for Cortex-X1C

[pratlucas]

Summary

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)

llvm/lib/Target/AArch64/AArch64.td

def ProcessorFeatures {
   list<SubtargetFeature> R82  = [HasV8_0rOps, FeaturePerfMon, FeatureFullFP16,
                                  FeatureFP16FML, FeatureSSBS, FeaturePredRes,
                                  FeatureSB];
   list<SubtargetFeature> X1   = [HasV8_2aOps, FeatureCrypto, FeatureFPARMv8,
                                  FeatureNEON, FeatureRCPC, FeaturePerfMon,
                                  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,
                                  FeatureFP16FML];
   list<SubtargetFeature> A64FX    = [HasV8_2aOps, FeatureFPARMv8, FeatureNEON,
                                      FeatureSHA2, FeaturePerfMon, FeatureFullFP16,
                                      FeatureSVE, FeatureComplxNum];
   list<SubtargetFeature> Carmel   = [HasV8_2aOps, FeatureNEON, FeatureCrypto,