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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269011 91177308-0d34-0410-b5e6-96231b3b80d8