The ACLE spec which describes these intrinsics hasn't been published yet, but this is based on the final draft which will be published soon, and these have already been implemented by GCC.
I think this looks OK.
Nit: I think it's obvious, but perhaps a comment here, which would be consistent with similar remarks in this file, that this this is for both A32 and A64 (and the one below A64 only)?
Yes, more modifiers! ;-)
Same nit as in of the other patches: not sure if we should spell out Armv8.2-A or if v8.2-A is actually ok.