[llvm] [AArch64] use `isTRNMask` to calculate shuffle costs (PR #171524)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

I think that either the generic ShuffleVectorInst::isTransposeMask should match transposes like this, or the isTRNMask can be reused in the same places we currently check isZipMask/isUZPMask/etc.

Can you add direct cost-modelling tests for shuffles of these kinds?

https://github.com/llvm/llvm-project/pull/171524