xfs use fs_holder_ops for the log and RT devices

Use the generic fs_holder_ops to shut down the file system when the
log or RT device goes away instead of duplicating the logic.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Message-Id: <20230802154131.2221419-13-hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>