python,sim,util: Move EmbeddedPython into it's own file.

By separating out this utility class, we make it possible to build
embedded python modules into other binarys without dragging along lots
of other, unrelated gem5 dependencies.

Also, move the class from sim/init.hh (which is a largely unrelated
name) to python/embedded.hh which much more directly describes what that
file contains.

Change-Id: Ia83439144893ad8401a5d51003e2686d9c9b2d7b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49418
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
8 files changed