[llvm] [RISCV] Add SMT_ prefix to XSMTVDot instructions. NFC (PR #154475)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/20822

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

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
7.858 [13/18/28] Linking CXX executable unittests/MC/MCTests
7.881 [12/18/29] Linking CXX executable unittests/ObjectYAML/ObjectYAMLTests
7.933 [11/18/30] Linking CXX executable unittests/Object/ObjectTests
8.098 [10/18/31] Linking CXX executable unittests/Analysis/AnalysisTests
8.314 [9/18/32] Linking CXX executable unittests/ObjCopy/ObjCopyTests
9.249 [8/18/33] Linking CXX executable unittests/ProfileData/ProfileDataTests
9.334 [7/18/34] Linking CXX executable unittests/Frontend/LLVMFrontendTests
9.368 [6/18/35] Linking CXX executable unittests/SandboxIR/SandboxIRTests
9.920 [5/18/36] Linking CXX executable unittests/XRay/XRayTests
10.527 [4/18/37] Linking CXX executable tools/lld/unittests/AsLibELF/LLDAsLibELFTests
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1211.569482

```

</details>

https://github.com/llvm/llvm-project/pull/154475