Codegen pass definition cleanup. No functionality.

Moving toward a uniform style of pass definition to allow easier target configuration.
Globally declare Pass ID.
Globally declare pass initializer.
Use INITIALIZE_PASS consistently.
Add a call to the initializer from CodeGen.cpp.
Remove redundant "createPass" functions and "getPassName" methods.

While cleaning up declarations, cleaned up comments (sorry for large diff).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150100 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/Hexagon/HexagonTargetMachine.cpp b/lib/Target/Hexagon/HexagonTargetMachine.cpp
index fb55f7d..1f7bdf0 100644
--- a/lib/Target/Hexagon/HexagonTargetMachine.cpp
+++ b/lib/Target/Hexagon/HexagonTargetMachine.cpp
@@ -120,7 +120,7 @@
 
 
 bool HexagonPassConfig::addPreSched2() {
-  PM.add(createIfConverterPass());
+  addPass(IfConverterID);
   return true;
 }