[mips] Fix emission of '.option pic0' for MIPS-IV.

Summary: This was a case of incorrect usage of hasMips64() vs isABI_N64()

Reviewers: matheusalmeida, dsanders

Reviewed By: dsanders

Differential Revision: http://reviews.llvm.org/D3398

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206388 91177308-0d34-0410-b5e6-96231b3b80d8