[PowerPC] Modern Book-E cores support sync

Older Book-E cores, such as the PPC 440, support only msync (which has the same
encoding as sync 0), but not any of the other sync forms. Newer Book-E cores,
however, do support sync, and for performance reasons we should allow the use
of the more-general form.

This refactors msync use into its own feature group so that it applies by
default only to older Book-E cores (of the relevant cores, we only have
definitions for the PPC440/450 currently).

llvm-svn: 218923
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.h b/llvm/lib/Target/PowerPC/PPCSubtarget.h
index 993afdf..9e4953f 100644
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -103,6 +103,7 @@
   bool HasPOPCNTD;
   bool HasLDBRX;
   bool IsBookE;
+  bool HasOnlyMSYNC;
   bool IsE500;
   bool IsPPC4xx;
   bool IsPPC6xx;
@@ -219,6 +220,7 @@
   bool hasPOPCNTD() const { return HasPOPCNTD; }
   bool hasLDBRX() const { return HasLDBRX; }
   bool isBookE() const { return IsBookE; }
+  bool hasOnlyMSYNC() const { return HasOnlyMSYNC; }
   bool isPPC4xx() const { return IsPPC4xx; }
   bool isPPC6xx() const { return IsPPC6xx; }
   bool isE500() const { return IsE500; }