aarch64: Optimise AdvSIMD log10f

aarch64: Optimise AdvSIMD log10f

Optimise AdvSIMD log10f by vectorising the special case.
Use scaling technique on subnormal values, then check for inf and
nan values.
The scaling technique will sqrt the input then multiply the output
by 2 because:
log(sqrt(x)) = 1/2(log(x)), so log(x) = 2log(sqrt(x))

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>