[clang] [Clang][AArch64] Add pessimistic vscale_range for sve/sme (PR #137624)

[Matthew Devereau via cfe-commits]

MDevereau wrote:

@efriedma-quic Is it OK for me to revert back to parsing the target-features string without using `getFunctionFeatureMap` as it appears to have a bug? 

https://github.com/llvm/llvm-project/pull/137624