[llvm] [NFC][ARM] Split SIMD identifier away from MVE (PR #130296)

[Jack Styles via llvm-commits]

Stylie777 wrote:

@davemgreen Regarding the failing test, this is actually fixed by a PR I had planned to follow this one, to make `+nosimd` operational. I am going to close this PR and merge these changes with the one that enables `+nosimd`. Its not ideal, I would rather they had been separate, but with the failing test it makes sense to do so as to not regress the behaviour of `+nosimd` (not that it works anyway).

https://github.com/llvm/llvm-project/pull/130296