[RISCV][LegalizeTypes] Try to expand BITREVERSE before promoting if the promoted...

[RISCV][LegalizeTypes] Try to expand BITREVERSE before promoting if the promoted BITREVERSE would expand anyway.

If we're going to end up expanding anyway, we should do it early
so we don't create extra operations to handle the bytes added by
promotion.

Simlilar was done for BSWAP previously.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D96681