add missing setattr methods

For the new truncate sequence every filesystem that wants to truncate on-disk
state needs a seattr method.  Convert the remaining filesystems that implement
the truncate inode operation to have its own setattr method.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>