[mips] Expand pseudo multiply/divide instructions in MipsCodeEmitter.cpp.

This patch fixes the following two tests which have been failing on
llvm-mips-linux builder since r178403:

LLVM :: Analysis/Profiling/load-branch-weights-ifs.ll
LLVM :: Analysis/Profiling/load-branch-weights-loops.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178584 91177308-0d34-0410-b5e6-96231b3b80d8