Add doInitialization/doFinalization to DataLayoutPass.

With this a DataLayoutPass can be reused for multiple modules.

Once we have doInitialization/doFinalization, it doesn't seem necessary to pass
a Module to the constructor.

Overall this change seems in line with the idea of making DataLayout a required
part of Module. With it the only way of having a DataLayout used is to add it
to the Module.

llvm-svn: 217548