benchmark: add benchmarks for `Buffer.from()`

Adds benchmarks for `Buffer.from()` and its various
argument combinations.

Ref: https://github.com/nodejs/node/issues/8733
PR-URL: https://github.com/nodejs/node/pull/8738


Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>