[mips] Implement sge/sgeu pseudo instructions

The `sge/sgeu Dst, Src1, Src2/Imm` pseudo instructions set register
`Dst` to 1 if register `Src1` is greater than or equal `Src2/Imm` and
to 0 otherwise.

Differential Revision: https://reviews.llvm.org/D64314

llvm-svn: 365476