x86-64: Add vector atanh/atanhf to libmvec microbenchmark

x86-64: Add vector atanh/atanhf to libmvec microbenchmark

Add vector atanh/atanhf and input files to libmvec microbenchmark.

libmvec-atanh-inputs:
  90% Normal random distribution
  range: (-1.0, 1.0)
  mean: 0.0
  sigma: 1.0
  10% uniform random distribution in range (-1.0, 1.0)

libmvec-atanhf-inputs:
  90% Normal random distribution
  range: (-1.0f, 1.0f)
  mean: 0.0f
  sigma: 1.0f
  10% uniform random distribution in range (-1.0f, 1.0f)

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>