9p: Enable multipage folios

Enable support for multipage folios on the 9P filesystem.  This is all
handled through netfslib and is already enabled on AFS and CIFS also.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: v9fs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Message-ID: <20240620173137.610345-7-dhowells@redhat.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>