[RISCV][LegalizeIntegerTypes] Teach PromoteSetCCOperands not to sext i32...

[RISCV][LegalizeIntegerTypes] Teach PromoteSetCCOperands not to sext i32 comparisons for RV64 if the promoted values are already zero extended.

This is similar to what is done for targets that prefer zero extend
where we avoid using a zero extend if the promoted values are sign
extended.

We'll also check for zero extended operands for ugt, ult, uge, and ule when the
target prefers sign extend. This is different than preferring zero extend, where
we only check for sign bits on equality comparisons.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D116421