stdlib: Move 'connect_things' to the AbstractBoard

This is in order to enforce a strict ordering of how gem5 components are
incorporated into a board. The `connect_things` function is now final so
it cannot be overridden.

Change-Id: I4c0e7ac9d307b399854f5326bb57bcf561f92054
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52183
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
5 files changed