[llvm] [RISCV] add computeKnownBitsForTargetNode for RISCVISD::SRLW (PR #155995)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

Please avoid force push unless necessary: https://llvm.org/docs/GitHub.html#rebasing-pull-requests-and-force-pushes

https://github.com/llvm/llvm-project/pull/155995