[Hexagon] Add intrinsics for data cache operations

This is the LLVM part, adding definitions for
  void @llvm.hexagon.Y2.dccleana(i8*)
  void @llvm.hexagon.Y2.dccleaninva(i8*)
  void @llvm.hexagon.Y2.dcinva(i8*)
  void @llvm.hexagon.Y2.dczeroa(i8*)
  void @llvm.hexagon.Y4.l2fetch(i8*, i32)
  void @llvm.hexagon.Y5.l2fetch(i8*, i64)
The clang part will follow.

llvm-svn: 308032