[MIPS] ST Loongson 2E/2F submission

[Ruan Beihong]

Loonsong also has some 3 oprands "imult" "idiv" "mod" instructions
which I can't find in the patches.
These instructions have lower latency and directly operate on GPR thus
no need to use HI LO.
I have done tests which showed these instruction really useful.

I think the authors of these patches must have seen those
instructions. I hope they will be seen in following patches.

Regards,
James Ruan