[RISCV] Add tests for existing (rotr (bswap X), (i32 16))->grevi pattern for...

[RISCV] Add tests for existing (rotr (bswap X), (i32 16))->grevi pattern for RV32. Extend same pattern to rotl and GREVIW.

Not sure why bswap was treated specially. This also applies to bitreverse
or generic grevi. We can improve this in future patches.
For now I just wanted to get the consistency and the test coverage
as I plan to make some other changes around bswap.