x86-64: Add vector expm1/expm1f to libmvec microbenchmark

x86-64: Add vector expm1/expm1f to libmvec microbenchmark

Add vector expm1/expm1f and input files to libmvec microbenchmark.

libmvec-expm1-inputs:
  90% Normal random distribution
  range: (-708.0, 709.0)
  mean: 0.0
  sigma: 16.0
  10% uniform random distribution in range (-500.0, 500.0)

libmvec-expm1f-inputs:
  90% Normal random distribution
  range: (-87.0f, 88.0f)
  mean: 0.0f
  sigma: 8.0f
  10% uniform random distribution in range (-50.0f, 50.0f)

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