Two small cleanups for ELF's templates.

* We only ever specialize these templates with an instantiation of ELFType,
  so we don't need a template template.
* Replace LLVM_ELF_COMMA with just passing the individual parameters to the
  macro. This requires a second macro for when we only have ELFT, but that
  is still a small win.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179726 91177308-0d34-0410-b5e6-96231b3b80d8