[llvm] [AArch64][TargetParser] move ArchInfo into tablegen [NFC] (PR #92037)

[Tomas Matheson via llvm-commits]

tmatheson-arm wrote:

> I might be wrong but as far as I understand the TargetParser keeps a list of default extensions per architecture (all the AEK_* entries) trying to model the implied subtarget features we have in tablegen. Since we are now unifying them I don't see the reason to duplicate this information in tablegen itself. We only need to pass the AEK_ equivalent (if it exists) for every implied subtarget feature in the targetparser emitter. I expect that the implied features and the default extensions differ for historical reasons therefore porting them may not be NFC.

I think they model two separate things and therefore probably need to remain separate lists:
- `SubtargetFeature::Implies` models mandatory feature dependencies
- default extensions for an architecture are those extensions which are enabled by default, but they are likely to be optional extensions and the user can disable them using `-march=...+noXYZ`


https://github.com/llvm/llvm-project/pull/92037