Revert "AMDGPU: enable 128-bit for local addr space under an option"

This reverts commit r329591.

It breaks various bots:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/16516
http://lab.llvm.org:8011/builders/clang-ppc64be-linux/builds/17374
http://lab.llvm.org:8011/builders/clang-ppc64le-linux/builds/15992
http://lab.llvm.org:8011/builders/clang-ppc64be-linux-lnt
http://lab.llvm.org:8011/builders/clang-ppc64le-linux-lnt/builds/11251
...

llvm-svn: 329610