Auto merge of #107294 - JamieCunliffe:neon-fp, r=Amanieu

Fix some issues with folded AArch64 features

In #91608 the `fp` feature was removed for AArch64 and folded into the `neon` feature, however disabling the `neon` feature doesn't actually disable the `fp` feature. If my understanding on that thread is correct it should do.

While doing this, I also noticed that disabling some features would disable features that it shouldn't. For instance enabling `sve` will enable `neon`, however, when disabling `sve` it would then also disable `neon`, I wouldn't expect disabling `sve` to also disable `neon`.

cc `@workingjubilee`

Author: bors