Convert to new override syntax

This is effectively a manual cherry-pick and squash of commits:

dd6fc5dcaa0a027b7651bb365d5dd0f623498f8f
917a82316bf53ead29d6345a39189d9e4efeef25
20e81c0a9d36660de671dd5ac2e006e31c0e621b

from the master branch with additional review and fixups.

The intent of these changes is to minimize the effort to backport
fixes from the master branch, which has been updated in preparation
for the switch to the next Yocto LTS release in early 2022.

Bug-AGL: SPEC-4144

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I91c1640c6335d7748a2531d2fe8bf86d2d2aee32
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26876
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>