## Summary
This PR enables Armv9-A as a supported target for torch.compile on AArch64 platforms. It extends the existing AArch64 backend configuration to recognize and properly generate code for Armv9-A CPUs. This PR replaces #175326 in favour of recent support of SVE 128.

## Implementation
+ Extend architecture detection logic for AArch64 to add Armv9-A to supported `-march` mappings
+ Ensure Inductor codegen correctly propagates the target triple and feature set
+ Preserve default behavior for non-Armv9-A environments
+ No behavior change for x86 or other architectures
+ 128-bit and 256-bit SVE support

## Testing
AArch64 Armv9-A hardware (Neoverse V2)
Verified:
+ `torch.compile` succeeds
+ Inductor-generated kernels compile without error

Pull Request resolved: https://github.com/pytorch/pytorch/pull/184555
Approved by: https://github.com/aditew01, https://github.com/jansel, https://github.com/jgong5