Update CHANGELOG
Update CHANGELOG

In moving to the shared HashiCorp release toolkit it was agreed to
remove support for the following architectures ppc64le mips mips64 mipsle mipsle64 s390x
since they are not part of the HashiCorp supported platforms. Nor are
they available as a release binary for any of the Packer plugins.

This change adds an entry to the Packer CHANGELOG to call out the
removal of the said architectures.

As we continue with the path of removing the plugins from Packer core
supporting platforms outside of those managed by our tooling
will be an issue for users as Packer needs the plugins to operate
properly.

hashicorp/packer,hashicorp/packer,hashicorp/packer,hashicorp/packer