contrib: aom: Disable SVE for Windows/aarch64 targets

SVE is, in general, not really supported on Windows yet; it's not exposed as a feature that can be detected via IsProcessorFeaturePresent. Backing up/restoring SVE registers in function prologues/epilogues is not supported by the SEH unwind info format yet either, which means that once functions written with intrinsics grow complex enough, they can end up requiring passing SVE types across functions, which requires SEH support.

Additionally, SVE registers are not supported in codeview (PDB) debug info yet either.

Therefore, just disable use of SVE when compiling libaom for Windows.

Toolchain issue report for reference: https://github.com/llvm/llvm-project/issues/80009