MAINTAINERS: add missing support status fields

This patch adds the "S:" line for areas of the codebase that currently
lack a support status field.

Note that there are a few more areas that are more abstract and do not
correspond to a specific set of files.  They have not been modified.

Cc: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190301163518.20702-1-stefanha@redhat.com
Message-Id: <20190301163518.20702-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>