Rename many DataLayout variables from TD to DL.

I am really sorry for the noise, but the current state where some parts of the
code use TD (from the old name: TargetData) and other parts use DL makes it
hard to write a patch that changes where those variables come from and how
they are passed along.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201827 91177308-0d34-0410-b5e6-96231b3b80d8