There are some Mips instructions that are lowered by the

assembler such as shifts greater than 32. In the case 
of direct object, the code gen needs to do this lowering 
since the assembler is not involved.

With the advent of the llvm-mc assembler, it also needs 
to do the same lowering.

This patch makes that specific lowering code accessible 
to both the direct object output and the assembler.

This patch does not affect generated output.

llvm-svn: 163287