aarch64: Optimise vecmath logs

* Transpose table layout for improved memory access
* Use half-vector special comparisons for AdvSIMD
* Improve register use near special-case branches
  - Due to the presence of a function call, return value would get
    mov-d out of x0 in order to facilitate PCS. By moving the final
    computation after the branch this can be avoided

Also change SVE routines to use overloaded intrinsics for readability.