Move TargetFrameLowering.h to CodeGen where it's implemented

This header already includes a CodeGen header and is implemented in
lib/CodeGen, so move the header there to match.

This fixes a link error with modular codegeneration builds - where a
header and its implementation are circularly dependent and so need to be
in the same library, not split between two like this.

llvm-svn: 317379
diff --git a/llvm/lib/Target/Mips/MipsFrameLowering.h b/llvm/lib/Target/Mips/MipsFrameLowering.h
index 8c4214c..883c326 100644
--- a/llvm/lib/Target/Mips/MipsFrameLowering.h
+++ b/llvm/lib/Target/Mips/MipsFrameLowering.h
@@ -15,7 +15,7 @@
 #define LLVM_LIB_TARGET_MIPS_MIPSFRAMELOWERING_H
 
 #include "Mips.h"
-#include "llvm/Target/TargetFrameLowering.h"
+#include "llvm/CodeGen/TargetFrameLowering.h"
 
 namespace llvm {
   class MipsSubtarget;