[clang] [llvm] [AArch64] Fix feature flags dependecies (PR #90612)

[Momchil Velikov via llvm-commits]

momchil-velikov wrote:

> > This patch removes FEAT_FPMR from list of available of architecture features, instead enabling FMPR register by default.
> 
> Can you expand a little bit on the reasoning? It doesn't seem all that problematic but is still eyebrow-raising.

The overall idea is that system registers ought be available everywhere without the need to explicitly enable them with a command line option. Since `FEAT_FPMR` has no function other than enabling the register and it is going to be enabled by default, having a command line option, predicate, feature definition, etc becomes pointless.

The FP8 instructions themselves are still guarded by a target feature.



https://github.com/llvm/llvm-project/pull/90612