[llvm] [TargetParser] Increase MAX_SUBTARGET_FEATURES to 384 (PR #144326)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave approved this pull request.

LGTM.
tangent question: now reading how `MAX_SUBTARGET_FEATURES` / `MAX_SUBTARGET_WORDS` are used, anyone know why we didn't use `BitVector` to implement `FeatureBitset`?

https://github.com/llvm/llvm-project/pull/144326