implement integer compare in mips fast-isel

Summary: implement SelectCmp (integer compare ) in mips fast-isel

Test Plan:
icmpa.ll
also ran 4 test-suite flavors mips32 r1/r2 O0/O2

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: llvm-commits, rfuhler, mcrosier

Differential Revision: http://reviews.llvm.org/D5566

llvm-svn: 219518