[llvm] [RISCV] Improve 2*XLEN SHL legalization with P extension. (PR #181056)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/38731

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR :: Dialect/SCF/ops.mlir (3856 of 3867)
PASS: MLIR :: Dialect/SparseTensor/sparse_vector.mlir (3857 of 3867)
PASS: MLIR :: mlir-tblgen/cpp-class-comments.td (3858 of 3867)
PASS: MLIR :: Pass/crash-recovery.mlir (3859 of 3867)
PASS: MLIR :: mlir-runner/utils.mlir (3860 of 3867)
PASS: MLIR :: Transforms/invalid-parallel-loop-collapsing.mlir (3861 of 3867)
PASS: MLIR :: Transforms/sccp-callgraph.mlir (3862 of 3867)
PASS: MLIR :: Pass/pass-timing.mlir (3863 of 3867)
PASS: MLIR :: Dialect/SCF/loop-unroll.mlir (3864 of 3867)
PASS: MLIR :: mlir-runner/simple.mlir (3865 of 3867)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1710.699226

```

</details>

https://github.com/llvm/llvm-project/pull/181056