x86-64: Create microbenchmark infrastructure for libmvec

Add python script to generate libmvec microbenchmark from the input
values for each libmvec function using skeleton benchmark template.

Creates double and float benchmarks with vector length 1, 2, 4, 8,
and 16 for each libmvec function.  Vector length 1 corresponds to
scalar version of function and is included for vector function perf
comparison.

Co-authored-by: Haochen Jiang <haochen.jiang@intel.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>