[RISCV] Add a guard condition to orc_b/brev8 handling in ReplaceNodeResults.

The orc_b and brev8 intrinsics are type overloaded, but only
i32 and XLen are supported types. The type legalization code in
ReplaceNodeResults only handles the i32 case on RV64. Add some
checks so we will fail type legalization for other types.