[RISCV] Use DIVUW/REMUW/DIVW instructions for i8/i16/i32 udiv/urem/sdiv when LHS is constant.

We don't really have optimizations for division with a constant
LHS. If we don't use a W instruction we end up needing to sign
or zero extend the RHS to use the 64-bit instruction.

I had to sign_extend i32 constants on the LHS instead of using
any_extend which becomes zero_extend. If we don't do this, constants
that were originally negative become harder to materialize. I think
this problem exists for more of our W instruction cases. For example
(i32 (shl -1, X)), but we don't have lit tests. I'll work on that
as a follow up.

I also left a FIXME for enabling W instruction for RHS constants
under -Oz.

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D105769