This adds support for Apple CPUs released since the last batch: apple-a15, apple-a16 and apple-m2.
They're roughly ARMv8.6. This works in the .td file, but in AArch64TargetParser.def, marking them v8.6 brings in support for the SM4 cryptographic hash and we don't actually have that. So TargetParser side they're marked as v8.5, with the extra features (BF16 and I8MM added manually).
Finally, A16 supports the HCX extension in addition to v8.6. This has no TargetParser implications.