[AArch64] Create a TargetInfo header.  NFC

Move the declarations of getThe<Name>Target() functions into a new header in
TargetInfo and make users of these functions include this new header.
This fixes a layering problem.

llvm-svn: 360709
diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index e18458f..0b52726 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -22,6 +22,7 @@
 #include "MCTargetDesc/AArch64MCExpr.h"
 #include "MCTargetDesc/AArch64MCTargetDesc.h"
 #include "MCTargetDesc/AArch64TargetStreamer.h"
+#include "TargetInfo/AArch64TargetInfo.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"