[RISCV] Fold binary op into select if profitable.

Consider the following pattern `binOp (select cond, x, c0), c1`.
Where `c0` and `c1` are constants.
We can transform it to `select cond, binOp(x, c1), binOp(c0, c1)`.

If `binOp(c0, c1)` ends up being `0` or `-1` we can turn the select into
a more profitable sequence.