[llvm] [RISCV] Add isel special case for (and (srl X, c2), c1) -> (slli_uw (srli x, c2+c3), c3). (PR #100966)

[Philip Reames via llvm-commits]

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

LGTM

(The discussion about a generic option can continue even if this lands.)

https://github.com/llvm/llvm-project/pull/100966