[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:

I've combined and simplified them into PNRtoPPRCopy.mir now.

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