bdev: add freeze and thaw holder operations

Add block device freeze and thaw holder operations. Follow-up patches
will implement block device freeze and thaw based on stuct
blk_holder_ops.

Link: https://lore.kernel.org/r/20231024-vfs-super-freeze-v2-4-599c19f4faac@kernel.org
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>