x86-64: Add vector exp/expf to libmvec microbenchmark

Add vector exp/expf and input files to libmvec microbenchmark.

libmvec-exp-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-expf-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>