[llvm] [AArch64][CostModel] Add SVE bfloat arithmetic tests (NFC) (PR #166951)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

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

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/42112

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

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
PASS: Flang :: Transforms/DoConcurrent/use_loop_bounds_in_body.f90 (3974 of 3984)
PASS: Flang :: Transforms/external-name-interop-symref-array.fir (3975 of 3984)
PASS: Flang :: Driver/fopenmp.f90 (3976 of 3984)
PASS: Flang :: Semantics/modfile73.f90 (3977 of 3984)
PASS: Flang :: Transforms/dlti-dependency.fir (3978 of 3984)
PASS: Flang :: Transforms/constant-argument-globalisation.fir (3979 of 3984)
PASS: Flang :: Transforms/debug-dwarf-version.fir (3980 of 3984)
PASS: Flang :: Driver/omp-driver-offload.f90 (3981 of 3984)
PASS: Flang :: Driver/linker-options.f90 (3982 of 3984)
PASS: Flang :: Intrinsics/math-codegen.fir (3983 of 3984)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2335.107099

```

</details>

https://github.com/llvm/llvm-project/pull/166951