x86-64: Add vector erf/erff to libmvec microbenchmark

x86-64: Add vector erf/erff to libmvec microbenchmark

Add vector erf/erff and input files to libmvec microbenchmark.

libmvec-erf-inputs:
  90% Normal random distribution
  range: (-6.0, 6.0)
  mean: 0.0
  sigma: 1.0
  10% uniform random distribution in range (-5.9, 5.9)

libmvec-erff-inputs:
  90% Normal random distribution
  range: (-4.0f, 4.0f)
  mean: 0.0f
  sigma: 1.0f
  10% uniform random distribution in range (-3.9f, 3.9f)

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