[llvm] [AArch64][CostModel] Updated inserelement/extractelement costs (PR #220627)

[Utpal Bora via llvm-commits]

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utpalbora wrote:

Without the `-aarch64-sve-vls-bfloat-support` flag, bfloats are costed differently. If we remove this RUN line, the cost difference will show up later when `-aarch64-sve-vls-bfloat-support` is enabled by default.
I am happy to remove it if this is acceptable.

https://github.com/llvm/llvm-project/pull/220627