Reorder includes in Target backends to following coding standards. Remove some superfluous forward declarations.

llvm-svn: 152997
diff --git a/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp b/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
index 07872d4..3d7ace5 100644
--- a/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
@@ -11,8 +11,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "HexagonRegisterInfo.h"
 #include "HexagonInstrInfo.h"
+#include "HexagonRegisterInfo.h"
 #include "HexagonSubtarget.h"
 #include "Hexagon.h"
 #include "llvm/ADT/STLExtras.h"