Implement floating point compare for mips fast-isel

Summary: Expand SelectCmp to handle floating point compare

Test Plan:
fpcmpa.ll
run 4 flavors of test-suite, mips32 r1/r2 O0/O2

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: llvm-commits, rfuhler

Differential Revision: http://reviews.llvm.org/D5567