Convert the autofs filesystem to use the mount API.

The conversion patch was originally written by David Howells.
I have taken that patch and broken it into several patches in an effort
to make the change easier to review.
Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Message-Id: <20230922041215.13675-8-raven@themaw.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>