[mips] Support 128-bit int in N32 ABI by overriding TargetInfo::hasInt128Type()

Summary: The condition in the base class is rather strange. It says a target has the 128-bit integer type if the size of a pointer is >= 64-bits. N32 has 32-bit pointers but 64-bit integers. I'm a bit reluctant to change this for all targets so this patch makes the method virtual and overrides it for MIPS64.

Reviewers: atanasyan

Reviewed By: atanasyan

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3472