x86-64: Add vector exp2/exp2f to libmvec microbenchmark

x86-64: Add vector exp2/exp2f to libmvec microbenchmark

Add vector exp2/exp2f and input files to libmvec microbenchmark.

libmvec-exp2-inputs:
  90% Normal random distribution
  range: (-1022.0, 1024.0)
  mean: 0.0
  sigma: 16.0
  10% uniform random distribution in range (-1000.0, 1000.0)

libmvec-exp2f-inputs:
  90% Normal random distribution
  range: (-126.0f, 128.0f)
  mean: 0.0f
  sigma: 8.0f
  10% uniform random distribution in range (-100.0f, 100.0f)

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