[llvm] [AArch64][Isel] For fixed length vectors use sve for bitreverse when available (PR #196025)

[Ricardo Jesus via llvm-commits]

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rj-jesus wrote:

Given the change above, I believe this is no longer needed?

The similar occurrence in the loop below could also be simplified, perhaps to `setOperationAction(ISD::BITREVERSE, {MVT::v8i8, MVT::v16i8}, Custom)` outside the loop, since it should now only be relevant for i8 vectors.

https://github.com/llvm/llvm-project/pull/196025