[llvm] [AArch64] recognise trn1/trn2 with flipped operands (PR #169858)

[Philip Ginsbach-Chen via llvm-commits]

ginsbach wrote:

> Yeah sounds good. Are you happy for it to be submitted?

Thank you. Yes, please go ahead and merge this for me (I do not have commit access).

https://github.com/llvm/llvm-project/pull/169858