[RISCV] Add a DAG combine for (czero_eq X, (xor Y, 1)) -> (czero_ne X, Y) if Y is 0 or 1.

This is an alternative to D155288 that can handle other sources of
xori like FP compares. Unfortunately, it misses the i64 setge case
on RV32 in condops.ll.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D155328