[llvm] [RISCV] Add isel special case for (and (shl X, c2), c1) -> (slli_uw (srli x, c4-c2), c4). (PR #91638)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM w/minor comment

https://github.com/llvm/llvm-project/pull/91638