CodeGen: Move TargetPassConfig from Passes.h to an own header; NFC

Many files include Passes.h but only a fraction needs to know about the
TargetPassConfig class. Move it into an own header. Also rename
Passes.cpp to TargetPassConfig.cpp while we are at it.

llvm-svn: 269011
diff --git a/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp b/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
index 97a4047d..45efb38 100644
--- a/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
+++ b/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
@@ -15,6 +15,7 @@
 #include "MSP430.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/Support/TargetRegistry.h"