[MCA] Remove dependency on CodeGen.

[orodley]

Summary

There isn't any actual dependency - there's one #include from CodeGen
but nothing from the header is actually used.

With this change we can use the MCA library from CodeGen without
circular dependencies (e.g. for scheduling).

[andreadb]

LGTM. Thanks!

llvm/trunk/tools/llvm-mca/lib/CMakeLists.txt

add_library(LLVMMCA
   Stages/InstructionTables.cpp
   Stages/RetireStage.cpp
   Stages/Stage.cpp
   Support.cpp
   )
 
 llvm_update_compile_flags(LLVMMCA)
 llvm_map_components_to_libnames(libs
-  CodeGen
   MC
   Support
   )
 
 target_link_libraries(LLVMMCA ${libs})
 set_target_properties(LLVMMCA PROPERTIES FOLDER "Libraries")

llvm/trunk/tools/llvm-mca/lib/LLVMBuild.txt

 ;   http://llvm.org/docs/LLVMBuild.html
 ;
 ;===------------------------------------------------------------------------===;
 
 [component_0]
 type = Library
 name = MCA
 parent = Libraries
-required_libraries = CodeGen MC Support
+required_libraries = MC Support

llvm/trunk/tools/llvm-mca/lib/Pipeline.cpp

 ///
 /// This file implements an ordered container of stages that simulate the
 /// pipeline of a hardware backend.
 ///
 //===----------------------------------------------------------------------===//
 
 #include "Pipeline.h"
 #include "HWEventListener.h"
-#include "llvm/CodeGen/TargetSchedule.h"
 #include "llvm/Support/Debug.h"
 
 namespace mca {
 
 #define DEBUG_TYPE "llvm-mca"
 
 using namespace llvm;