[llvm] [AArch64] Separate PNR into its own Register Class (PR #65306)

[Matthew Devereau via llvm-commits]

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+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
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MDevereau wrote:

The logic was they're both from organic examples. For example in `sve2p1-intrinsics-predicate-as-counter.ll` the pext tests will generate a PPR->PNR copy while the ptrue tests in that file will generate a PNR->PPR copy. If you'd rather I combine them into a single file and make them near carbon copies of each other that's fine by me.

https://github.com/llvm/llvm-project/pull/65306