[AArch64][SVE2] Rename bitperm feature to sve2-bitperm

Summary:
The bitperm feature flag is now prefixed with SVE2, as it is for all other SVE2
extensions

Patch by Maciej Gabka.

Reviewers: sdesmalen, rovka, chill, SjoerdMeijer, rengolin

Reviewed By: SjoerdMeijer, rengolin

Differential Revision: https://reviews.llvm.org/D65327

llvm-svn: 367124
diff --git a/llvm/lib/Support/AArch64TargetParser.cpp b/llvm/lib/Support/AArch64TargetParser.cpp
index df4caa1..6f1d6d5 100644
--- a/llvm/lib/Support/AArch64TargetParser.cpp
+++ b/llvm/lib/Support/AArch64TargetParser.cpp
@@ -96,8 +96,8 @@
     Features.push_back("+sve2-sm4");
   if (Extensions & AEK_SVE2SHA3)
     Features.push_back("+sve2-sha3");
-  if (Extensions & AEK_BITPERM)
-    Features.push_back("+bitperm");
+  if (Extensions & AEK_SVE2BITPERM)
+    Features.push_back("+sve2-bitperm");
   if (Extensions & AEK_RCPC)
     Features.push_back("+rcpc");