[mips] The decision between GOT_DISP and GOT16 for global addresses depends on ABI rather than MIPS64

Summary: No functional change (for supported use cases)

Reviewers: matheusalmeida

Reviewed By: matheusalmeida

Differential Revision: http://llvm-reviews.chandlerc.com/D3191

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204922 91177308-0d34-0410-b5e6-96231b3b80d8